Stripe's webhook docs are good. They tell you to verify signatures, handle checkout.session.completed, and return 200 fast. What they don't emphasize enough: Stripe will retry failed webhooks up to 72 hours. If your server returned a 500, that event is coming back. Your handler must be idempotent.
What idempotency means for webhooks
Idempotent: processing the same event N times produces the same result as processing it once.
Non-idempotent webhook handler bugs I've seen in the wild:
- Duplicate subscription creation (user gets charged twice, gets two accounts)
- Double email sends ("Your account is ready" × 2)
- Race condition where two workers process the same event simultaneously
- Counter increments that fire twice (
usage_count += 1runs twice = wrong count)
All of these are fixable with one pattern: event deduplication.
The complete webhook handler
// app/api/webhooks/stripe/route.ts
import { NextRequest, NextResponse } from 'next/server';
import Stripe from 'stripe';
import { db } from '@/db';
import { webhookEvents, subscriptions } from '@/db/schema';
import { eq } from 'drizzle-orm';
const stripe = new Stripe(process.env.STRIPE_SECRET_KEY!, {
apiVersion: '2024-12-18.acacia',
});
export async function POST(req: NextRequest) {
const body = await req.text();
const sig = req.headers.get('stripe-signature')!;
let event: Stripe.Event;
// Step 1: Verify the signature
try {
event = stripe.webhooks.constructEvent(
body,
sig,
process.env.STRIPE_WEBHOOK_SECRET!
);
} catch (err) {
console.error('Webhook signature verification failed:', err);
return NextResponse.json({ error: 'Invalid signature' }, { status: 400 });
}
// Step 2: Idempotency check — have we processed this event before?
const existing = await db.query.webhookEvents.findFirst({
where: eq(webhookEvents.stripeEventId, event.id),
});
if (existing) {
// Already processed — return 200 so Stripe stops retrying
console.log(`Duplicate event ${event.id} — skipping`);
return NextResponse.json({ received: true, duplicate: true });
}
// Step 3: Record the event as being processed (BEFORE processing)
await db.insert(webhookEvents).values({
stripeEventId: event.id,
type: event.type,
status: 'processing',
receivedAt: new Date(),
});
// Step 4: Handle the event
try {
await handleEvent(event);
// Mark as complete
await db.update(webhookEvents)
.set({ status: 'completed', processedAt: new Date() })
.where(eq(webhookEvents.stripeEventId, event.id));
} catch (error) {
// Mark as failed — but still return 200 for non-retriable errors
await db.update(webhookEvents)
.set({
status: 'failed',
error: error instanceof Error ? error.message : String(error),
processedAt: new Date(),
})
.where(eq(webhookEvents.stripeEventId, event.id));
// Return 500 only for retriable errors (transient failures)
// Return 200 for permanent failures (bad data, etc.) to stop retries
const isRetriable = error instanceof Error &&
error.message.includes('ECONNRESET');
if (isRetriable) {
// Delete the event record so Stripe can retry and we'll try again
await db.delete(webhookEvents)
.where(eq(webhookEvents.stripeEventId, event.id));
return NextResponse.json({ error: 'Processing failed' }, { status: 500 });
}
}
return NextResponse.json({ received: true });
}
The webhook_events table schema
// db/schema.ts
import { pgTable, text, timestamp, uuid } from 'drizzle-orm/pg-core';
export const webhookEvents = pgTable('webhook_events', {
id: uuid('id').primaryKey().defaultRandom(),
stripeEventId: text('stripe_event_id').notNull().unique(), // unique prevents duplicates
type: text('type').notNull(),
status: text('status').notNull(), // processing | completed | failed
error: text('error'),
receivedAt: timestamp('received_at').notNull(),
processedAt: timestamp('processed_at'),
});
The unique() on stripe_event_id is your last-resort safety net — even if two workers check simultaneously and both pass the duplicate check, only one INSERT will succeed. The other throws a unique constraint violation.
Handling each event type safely
async function handleEvent(event: Stripe.Event) {
switch (event.type) {
case 'checkout.session.completed':
await handleCheckoutComplete(event.data.object as Stripe.Checkout.Session);
break;
case 'customer.subscription.updated':
await handleSubscriptionUpdate(event.data.object as Stripe.Subscription);
break;
case 'customer.subscription.deleted':
await handleSubscriptionCancel(event.data.object as Stripe.Subscription);
break;
case 'invoice.payment_failed':
await handlePaymentFailed(event.data.object as Stripe.Invoice);
break;
default:
console.log(`Unhandled event type: ${event.type}`);
}
}
checkout.session.completed — the critical one
async function handleCheckoutComplete(session: Stripe.Checkout.Session) {
const userId = session.metadata?.userId;
if (!userId) throw new Error(`No userId in session metadata: ${session.id}`);
// Idempotent upsert — if subscription already exists, update it
await db.insert(subscriptions)
.values({
userId,
stripeCustomerId: session.customer as string,
stripeSubscriptionId: session.subscription as string,
status: 'active',
plan: session.metadata?.plan ?? 'pro',
createdAt: new Date(),
})
.onConflictDoUpdate({
target: subscriptions.userId, // or stripeSubscriptionId
set: {
status: 'active',
stripeSubscriptionId: session.subscription as string,
},
});
// Send welcome email — make this idempotent too
await sendWelcomeEmail(userId, { once: true }); // internal dedup by userId
}
onConflictDoUpdate is the Drizzle equivalent of INSERT ... ON CONFLICT DO UPDATE. Safe to run twice.
subscription.updated — be careful with status
async function handleSubscriptionUpdate(subscription: Stripe.Subscription) {
// Fetch the full subscription from Stripe — webhook data can be stale
// especially on retries
const fresh = await stripe.subscriptions.retrieve(subscription.id);
await db.update(subscriptions)
.set({
status: fresh.status,
currentPeriodEnd: new Date(fresh.current_period_end * 1000),
cancelAtPeriodEnd: fresh.cancel_at_period_end,
})
.where(eq(subscriptions.stripeSubscriptionId, subscription.id));
}
Always re-fetch from Stripe on updates. Retried webhooks carry the state from when the event first fired — the subscription may have changed again since then.
Race condition protection
The status: 'processing' insert + unique constraint handles races:
Worker A: INSERT webhook_event (id=evt_123, status=processing) ← succeeds
Worker B: INSERT webhook_event (id=evt_123, status=processing) ← unique violation
Worker B: catches error, returns 200 (safe — Worker A has it)
Worker A: processes event, updates status=completed
For extra safety with high-throughput systems, use a database-level advisory lock:
async function processWithLock(eventId: string, fn: () => Promise<void>) {
// Postgres advisory lock — only one worker processes at a time
const lockKey = hashCode(eventId); // convert to int32
await db.execute(sql`SELECT pg_advisory_lock(${lockKey})`);
try {
await fn();
} finally {
await db.execute(sql`SELECT pg_advisory_unlock(${lockKey})`);
}
}
Testing your webhook handler locally
# Install Stripe CLI
brew install stripe/stripe-cli/stripe
# Forward events to your local server
stripe listen --forward-to localhost:3000/api/webhooks/stripe
# Trigger a test event
stripe trigger checkout.session.completed
# Test idempotency: send the same event twice
stripe events resend evt_1234567890 # resend a specific event
Always test your handler by resending the same event twice before shipping to production.
The webhook events table as audit log
Bonus: your webhook_events table is now a full audit log. For compliance or debugging:
// Show all payment events for a customer
const events = await db.query.webhookEvents.findMany({
where: and(
like(webhookEvents.type, 'invoice.%'),
eq(webhookEvents.status, 'completed')
),
orderBy: desc(webhookEvents.receivedAt),
limit: 50,
});
When a user says "I got charged twice" — you check the table. Every event, every status, every error, timestamped.
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