How to follow a channel in Node.js with the Wapito WhatsApp API

// Follow Channels with the Wapito WhatsApp API.
//
// Search or resolve a link, verify it is the right channel, page back through the history, then handle new posts from the webhook.
//
// Run it with:
//   export WAPITO_TOKEN="wpt_..."
//   node follow-channels.mjs

const BASE_URL = 'https://api.wapito.com/v1';
const TOKEN = process.env.WAPITO_TOKEN;

// --- Search the directory ---
{
  const url = BASE_URL + '/newsletters/find?q=release%20notes&country=GB&count=50';
  const options = {method: 'GET', headers: {Authorization: 'Bearer ' + TOKEN}};

  try {
    const response = await fetch(url, options);
    const data = await response.json();
    console.log(data);
  } catch (error) {
    console.error(error);
  }
}

// --- Resolve an invite link ---
{
  const url = BASE_URL + '/newsletters/invite/0029VaAbCdEfGhIjKlMnOp';
  const options = {method: 'GET', headers: {Authorization: 'Bearer ' + TOKEN}};

  try {
    const response = await fetch(url, options);
    const data = await response.json();
    console.log(data);
  } catch (error) {
    console.error(error);
  }
}

// --- Read what has been published ---
{
  const url = BASE_URL + '/newsletters/120363099887766554@newsletter/messages?count=50&offset=0';
  const options = {method: 'GET', headers: {Authorization: 'Bearer ' + TOKEN}};

  try {
    const response = await fetch(url, options);
    const data = await response.json();
    console.log(data);
  } catch (error) {
    console.error(error);
  }
}

import crypto from 'node:crypto';
import express from 'express';

const app = express();
const SECRET = process.env.WAPITO_WEBHOOK_SECRET;
const EVENTS = new Set(['messages']);

/** Checks the X-Wapito-Signature header: t=<ms>,v1=<hex hmac-sha256>. */
function verify(raw, header) {
  if (!header) return false;
  const parts = Object.fromEntries(header.split(',').map((p) => p.split('=')));
  if (!parts.t || !parts.v1) return false;
  if (Math.abs(Date.now() - Number(parts.t)) > 300_000) return false; // 5 minute clock skew
  const expected = crypto.createHmac('sha256', SECRET).update(`${parts.t}.`).update(raw).digest('hex');
  const a = Buffer.from(expected, 'hex');
  const b = Buffer.from(parts.v1, 'hex');
  return a.length === b.length && crypto.timingSafeEqual(a, b);
}

app.post('/wapito', express.raw({ type: 'application/json' }), (req, res) => {
  if (!verify(req.body, req.get('X-Wapito-Signature'))) return res.sendStatus(401);
  const payload = JSON.parse(req.body.toString('utf8'));
  if (EVENTS.has(payload.event)) console.log(payload.event, payload.data);
  res.sendStatus(200); // answer 2xx fast; do the real work in a queue
});

app.listen(Number(process.env.PORT ?? 3000));