OP Mainnet 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": "optimism",
    "direction": "in",
    "type": "token",
    "transaction_hash": "0xde65ec4246332db41cca7eef7001f80e2064bcd1bb4abb3924188bf4c9e32a19",
    "transfer_index": 9,
    "block_number": 158495252,
    "block_hash": "0x6d7a74b7c7cad66be99411a890577972934996cdce9e78cc56ec7d7ddf2d5f00",
    "block_timestamp": "2026-10-02T09:41:05Z",
    "confirmations": 20,
    "from": "0x5bf5a1da194ed738308ecbfcfa38f6e1dc50ace5",
    "to": "0x70598e346eb9a0653f0319cbce139f5a03e00d98",
    "currency": "USDC",
    "amount": "250",
    "amount_raw": "250000000",
    "decimals": 6,
    "contract_address": "0x0b2c639c533813f4aa9d7837caf62653d097ff85"
  }
}

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);
  },
);