sonoff-lan-mode-test.js

const WebSocket = require('ws');

// Turns out you don't need to dump packets at all - you don't even need a valid API key or device ID when it's in LAN mode.
// All you need to know is the IP address of the device, as it happily accepts WebSocket messages with any string as the "apikey".
const IPADDRESS = '192.168.0.72';

const seq = () => String(Date.now());
const ws = new WebSocket('ws://' + IPADDRESS + ':8081', [ 'chat' ]);
const nonce = 'nonce';

// Log all messages received from the device
ws.on('message', function incoming(json) {
  const messageData = JSON.parse(json);
  console.log('Received Message: %j', messageData);
});

// Define method to send update message to change switch state
function updateState(newState) {
  const updateMessageJSON = JSON.stringify({
    "action": "update",
    "deviceid": nonce,
    "apikey": nonce,
    "selfApikey": nonce,
    "params": {
      "switch": newState
    },
    "sequence": seq(),
    "userAgent": "app"
  });

  console.log('Sending Update Message: %s', updateMessageJSON);
  ws.send(updateMessageJSON);
}

// Initiate session with device in LAN mode by sending "userOnline" action message
ws.on('open', function initiateSession(ev) {
  const initiateSessionMessageJSON = JSON.stringify({
    "action":    "userOnline",
    "ts":        String(0 | Date.now / 1000),
    "version":   6,
    "apikey":    nonce,
    "sequence":  seq(),
    "userAgent": "app"
  });
  
  console.log('Sending User Online Message: %s', initiateSessionMessageJSON);
  ws.send(initiateSessionMessageJSON);
});

function switchOn() {
  console.log('Switching On');
  updateState('on');
}

function switchOff() {
  console.log('Switching Off');
  updateState('off');
}

function switchOnFor5Seconds() {
  switchOn();
  setTimeout(switchOff, 5000);
}

setInterval(switchOnFor5Seconds, 10000);