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HTTP callbacks for real-time inter-application communication

Core Idea: Webhooks are user-defined HTTP callbacks that are triggered by events in a source system, enabling real-time data transfer between applications without requiring polling.

Key Elements

Key Features

• Event-driven architecture
• Real-time data transmission
• HTTP/HTTPS protocol based
• Customizable payload formats
• User-defined endpoint registration
• Stateless communication model

Technical Specifications

• Uses standard HTTP methods (typically POST)
• JSON or XML payloads common
• Authentication via tokens, HMAC signatures, or OAuth
• Retry mechanisms for delivery failure
• Asynchronous communication pattern
• Webhook URLs are registered with the source system

Implementation Patterns

Provider Side (Sending Webhooks)

1. Define triggerable events in your system
2. Allow users to register webhook URLs
3. Generate payloads when events occur
4. Send HTTP requests to registered endpoints
5. Handle delivery failures and retries

Consumer Side (Receiving Webhooks)

1. Create an HTTP endpoint to receive webhook data
2. Implement authentication validation
3. Process the incoming payload
4. Respond with appropriate HTTP status code
5. Execute business logic based on the event

Security Considerations

• Verify webhook authenticity through signatures
• Use HTTPS for all webhook traffic
• Implement payload validation
• Apply rate limiting
• Consider IP whitelisting
• Use timebound tokens

Code Example: Webhook Signature Verification (Node.js)

const crypto = require('crypto');

function verifyWebhook(payload, signature, secret) {
  const expectedSignature = crypto
    .createHmac('sha256', secret)
    .update(payload)
    .digest('hex');
  
  return crypto.timingSafeEqual(
    Buffer.from(signature),
    Buffer.from(expectedSignature)
  );
}

// Express route handling GitHub webhooks
app.post('/github-webhook', (req, res) => {
  const signature = req.headers['x-hub-signature-256'].split('sha256=')[1];
  const payload = JSON.stringify(req.body);
  const isValid = verifyWebhook(payload, signature, process.env.WEBHOOK_SECRET);
  
  if (!isValid) {
    return res.status(401).send('Invalid signature');
  }
  
  // Process the webhook event
  const event = req.headers['x-github-event'];
  console.log(`Received ${event} event`);
  
  // Handle the event
  if (event === 'push') {
    // Handle push event
  }
  
  res.status(200).send('Webhook received');
});

Common Use Cases

• CI/CD pipeline triggers
• Payment processing notifications
• CRM and marketing automation
• Chat and messaging integrations
• E-commerce order updates
• IoT device event notifications
• Content management system updates

Additional Connections

• Broader Context: Event-Driven Architecture (webhooks are an implementation)
• Applications: API Integration Patterns, Microservices Communication
• See Also: Server-Sent Events, WebSockets, Polling vs Pushing

References

1. "Web API Design" by Brian Mulloy
2. "Building Event-Driven Microservices" by Adam Bellemare

#api #integration #web-development #event-driven #architecture

Connections:

Sources:

• From: Worklog n8n