Next.js Stripe Webhook Handler

handler.ts

import { NextApiRequest, NextApiResponse } from 'next';
import Stripe from 'stripe';
import { Readable } from 'node:stream';

export const config = {
  api: {
    bodyParser: false,
  },
};

async function buffer(readable: Readable) {
  const chunks = [];
  for await (const chunk of readable) {
    chunks.push(typeof chunk === 'string' ? Buffer.from(chunk) : chunk);
  }
  return Buffer.concat(chunks);
}

const stripe = new Stripe(process.env.STRIPE_SECRET_KEY, {
  apiVersion: '2020-08-27',
});

const relevantEvents = new Set(['customer.subscription.created']);

export default async function handler(req: NextApiRequest, res: NextApiResponse) {
  if (req.method === 'POST') {
    const buf = await buffer(req);
    const sig = req.headers['stripe-signature'];
    const webhookSecret = process.env.STRIPE_WEBHOOK_SECRET;
    let event: Stripe.Event;

    try {
      if (!sig || !webhookSecret) return;
      event = stripe.webhooks.constructEvent(buf, sig, webhookSecret);
    } catch (err: any) {
      console.log(`❌ Error message: ${err.message}`);
      return res.status(400).send({ message: `Webhook Validation Error: ${err.message}` });
    }

    if (relevantEvents.has(event.type)) {
      try {
        switch (event.type) {
          case 'customer.subscription.created':
            // TODO: handle event
            break;
          default:
            console.log(`Unhandled event type: ${event.type}`);
            break;
        }
      } catch (error) {
        console.log(error);
        return res.status(400).send({ message: `Webhook Handler Error: ${error}` });
      }
    }

    res.json({ received: true });
  } else {
    res.setHeader('Allow', 'POST');
    return res.status(405).end('Method Not Allowed');
  }
}