FB-subscribe-hook.js

// Verify with FB console.
app.get('/fb-subscribe', (req, res, next) => {
  if (req.param('hub.mode') == 'subscribe' && req.param('hub.verify_token') == process.env.VERIFY_TOKEN) {
    res.send(req.param('hub.challenge'));
  } else {
    res.sendStatus(400);
  }
});
// Subscriber for receiving FB notification.
app.post('/fb-subscribe',
  // Middleware for authorization.
  (req, res, next) => {
    if (req.isXHub && req.isXHubValid()) {
      return next();
    } else {
      res.sendStatus(401);
    }
  },
  (req, res) => {
    const { entry, object } = req.body;
    if (object === 'page') {
      entry.forEach((eachEntry) => {
        const { changes } = eachEntry;
        changes.forEach((change) => {
          const { field, value: { sender_name, sender_id, item, post_id, verb, message } } = change;
          // Handle feed
          if (field === 'feed') {
            // Add new comment into redis and broadcast to subscribers.
            if (item === 'comment' && verb === 'add') {
              const videoId = post_id.split('_')[1];
              const redis = createClient(redisUrl);
              redis.rpush(`live:${videoId}:comments`, message);
              redis.publish(`live:${videoId}:comments:latest`, message);
              redis.quit();
            }
          }
        });
      });
    }
    res.send('OK');
  }
);