Polygon USDC transfer notifications, delivered as webhooks

POST /webhooks/chainhook HTTP/1.1
Host: api.example.com
Content-Type: application/json
User-Agent: chainhook/1.x
X-Webhook-Id: 01a0fbfd-4fe4-7a3c-8f21-6b9d0e4c7a15
X-Webhook-Signature: 7a12d02673420517279805cf8188a1a62c6f69706161ba5cf0a8ec91ea66b8e3

{
  "id": "01a0fbfd-4fe4-7a3c-8f21-6b9d0e4c7a15",
  "event": "transfer.detected",
  "created_at": "2026-10-02T09:41:17Z",
  "webhook_id": "01a0fbf2-fadc-7c3e-9b1a-4d6f2e8a5c71",
  "data": {
    "network": "polygon",
    "direction": "in",
    "type": "token",
    "transaction_hash": "0x1dfd88322a841e601026f788db63da3e2a78fa6f6ffab51d547ce2586b688837",
    "transfer_index": 77,
    "block_number": 95905588,
    "block_hash": "0xfd008737391bea47c5ee46fe218ecdbeb17e4192d8b409802cf016d1efb51be2",
    "block_timestamp": "2026-10-02T09:41:05Z",
    "confirmations": 64,
    "from": "0xf716df5d2223b8bbabdfe7a677d970c263745ee5",
    "to": "0xc47ac81bea5ea48a2e2b0123b362e0ced64fe357",
    "currency": "USDC",
    "amount": "75",
    "amount_raw": "75000000",
    "decimals": 6,
    "contract_address": "0x2791bca1f2de4661ed88a30c99a7a9449aa84174"
  }
}

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

const app = express();

app.post(
  '/webhooks/chainhook',
  express.raw({ type: 'application/json' }),
  (req, res) => {
    const signature = req.get('X-Webhook-Signature') ?? '';
    const expected = crypto
      .createHmac('sha256', process.env.CHAINHOOK_SIGNING_SECRET)
      .update(req.body)
      .digest('hex');

    const valid =
      signature.length === expected.length &&
      crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected));

    if (!valid) {
      return res.sendStatus(401);
    }

    const event = JSON.parse(req.body);
    // Skip event.id if you've already processed it.

    res.sendStatus(200);
  },
);