Building Real-Time Event-Driven Applications with FluxRail: A Step-by-Step Guide

Introduction

The blockchain world is inherently event-driven. Transactions, transfers, and smart contract interactions happen asynchronously, and applications need to react in real time. FluxRail's Core product provides a unified API to monitor blockchain events across 36+ chains, delivering them to your backend via signed webhooks. In this guide, you'll learn how to build a real-time event-driven application using FluxRail—from subscribing to addresses to processing webhooks securely.

Prerequisites

• A FluxRail account (sign up at fluxrail.io)
• A test API key (flux_test_...) from the dashboard
• A public endpoint to receive webhooks (e.g., a server with HTTPS, or a tool like ngrok for local development)

Step 1: Create a Webhook Endpoint

First, register the URL where FluxRail will send events. Use the POST /api/v1/webhooks endpoint.

curl -X POST https://api.fluxrail.io/api/v1/webhooks \
  -H "X-API-Key: flux_test_YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "url": "https://your-server.com/webhooks/fluxrail",
    "description": "My production webhook",
    "events": ["transaction.mined", "transfer.sent"]
  }'

The response includes an id and a secret used for signature verification. Save the secret securely.

Step 2: Subscribe to an Address

Now, monitor a blockchain address. Use POST /api/v1/subscriptions.

curl -X POST https://api.fluxrail.io/api/v1/subscriptions \
  -H "X-API-Key: flux_test_YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "address": "0x742d35Cc6634C0532925a3b844Bc9e7595f2bD18",
    "chain": "ethereum",
    "webhook_url": "https://your-server.com/webhooks/fluxrail",
    "events": ["transaction.mined", "token.transfer"]
  }'

FluxRail will now stream events for that address to your webhook.

Step 3: Verify Webhook Signatures

Every webhook request includes a X-FluxRail-Signature header. Verify it using HMAC SHA-256 with your webhook secret to ensure the payload is authentic.

Example in Node.js:

const crypto = require('crypto');

function verifyFluxRailSignature(req, secret) {
  const signature = req.headers['x-fluxrail-signature'];
  const payload = JSON.stringify(req.body);
  const expected = crypto
    .createHmac('sha256', secret)
    .update(payload)
    .digest('hex');
  return crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected));
}

Always use timingSafeEqual to prevent timing attacks.

Step 4: Handle Events

FluxRail sends events as JSON. Here's a typical transaction.mined payload:

{
  "id": "evt_abc123",
  "type": "transaction.mined",
  "created": 1712345678,
  "data": {
    "chain": "ethereum",
    "hash": "0xabcdef...",
    "from": "0x...",
    "to": "0x...",
    "value": "1000000000000000000",
    "block_number": 19000000,
    "confirmations": 12
  }
}

Process the event in your application—update a database, trigger a payout, or send a notification. Respond with 200 OK to acknowledge receipt. FluxRail will retry on non-200 responses.

Step 5: Monitor Subscription Health

Check your subscription's status and webhook delivery logs.

curl https://api.fluxrail.io/api/v1/subscriptions/YOUR_SUBSCRIPTION_ID \
  -H "X-API-Key: flux_test_YOUR_API_KEY"

View webhook logs for a subscription:

curl https://api.fluxrail.io/api/v1/subscriptions/YOUR_SUBSCRIPTION_ID/webhook-logs \
  -H "X-API-Key: flux_test_YOUR_API_KEY"

Step 6: Combine with FluxRail Pay for Gas-Free Transfers

React to an event by sending a gas-free transfer using FluxRail Pay. For example, when a deposit is detected, automatically issue a payout.

curl -X POST https://api.fluxrail.io/api/v1/transfer \
  -H "X-API-Key: flux_test_YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "0xYourSenderAddress",
    "to": "0xRecipientAddress",
    "token": "USDC",
    "network": "ERC20",
    "amount": "50.00",
    "sponsor_gas": true
  }'

FluxRail covers the gas fees via its paymaster infrastructure.

Step 7: Scale with Bulk Subscriptions

To monitor many addresses at once, use the bulk endpoint.

curl -X POST https://api.fluxrail.io/api/v1/subscriptions/bulk \
  -H "X-API-Key: flux_test_YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "subscriptions": [
      {"address": "0x...", "chain": "ethereum", "webhook_url": "..."},
      {"address": "0x...", "chain": "polygon", "webhook_url": "..."}
    ]
  }'

Best Practices

• Idempotency: Events may be delivered more than once. Use the event id to deduplicate.
• Fast Response: Acknowledge webhooks immediately (< 5s). Offload heavy processing to a queue.
• Retry Logic: If your endpoint fails, FluxRail retries with exponential backoff. Monitor delivery logs.
• Test Mode: Use flux_test_ keys for development. All events are simulated but follow the same lifecycle.

Conclusion

You've built a real-time event-driven application with FluxRail in minutes. By combining Core's blockchain monitoring with Pay's gas-free transfers, you can automate complex workflows—from DeFi bots to cross-border payment triggers. Explore the full API at docs.fluxrail.io and join the future of unified blockchain infrastructure.