TradeTracker redirect handler for node.js

handler.js

// Tradetracker Direct Linking Redirect Page.
// https://sc.tradetracker.net/implementation/overview?f%5Btarget%5D=&f%5Bname%5D=General&f%5Bversion%5D=All&f%5BversionInfo%5D=Redirect
const crypto = require('crypto');

// Set domain name on which the redirect-page runs, WITHOUT "www.".
const DOMAIN_NAME = '';
// Set tracking group ID if provided by TradeTracker.
const TRACKING_GROUP_ID = '';
// Don't change this line
const ONE_YEAR_IN_SECS = 31536000;

const handler = async (req, res) => {
  const { tt, r: redirectUrl = '' } = req.query;

  // Set the P3P compact policy.
  res.setHeader('P3P', 'CP="IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT"');

  if (!tt) {
    res.writeHead(301, { Location: '/' });
    return res.end();
  }

  const trackingParams = tt.split('_');
  const [campaignId = '', materialId = '', affiliateId = '', reference = ''] = trackingParams;
  // Calculate MD5 checksum.
  const checkSum = crypto
    .createHash('md5')
    .update(`CHK_${campaignId}::${materialId}::${materialId}::${reference}`)
    .digest('hex');
  const timestamp = Math.floor(new Date().getTime() / 1000);
  // Set tracking data.
  const trackingData = encodeURIComponent(
    `${materialId}::${affiliateId}::${reference}::${checkSum}::${timestamp}`
  );
  const cookyExpiresAt = new Date(Date.now() + ONE_YEAR_IN_SECS * 1000).toUTCString();

  res.setHeader('Set-Cookie', [
    // Set regular tracking cookie.
    `TT2_${campaignId}=${trackingData}; Expires=${cookyExpiresAt}; Max-Age=${ONE_YEAR_IN_SECS}; Path=/; Domain=.${DOMAIN_NAME}`,
    // Set session tracking cookie.
    `TTS_${campaignId}=${trackingData}; Path=/; Domain=.${DOMAIN_NAME}`,
    // Set tracking group cookie, if any
    ...(TRACKING_GROUP_ID.length > 0
      ? [
          `__tgdat${TRACKING_GROUP_ID}=${trackingData}_${campaignId}; Expires=${cookyExpiresAt}; Max-Age: ${ONE_YEAR_IN_SECS}; Path=/; Domain=.${DOMAIN_NAME}`,
        ]
      : []),
  ]);

  // Set track-back URL.
  const trackBackUrl = `https://tc.tradetracker.net/?c=${campaignId}&m=${materialId}&a=${affiliateId}&r=${encodeURIComponent(
    reference
  )}&u=${encodeURIComponent(redirectUrl)}`;

  // Redirect to TradeTracker.
  res.writeHead(301, { Location: trackBackUrl });
  // res.setHeader('Location', trackBackUrl);
  return res.end();
};

module.exports = handler;