API Development and Integration

Chapter 13: API Integration Patterns

13.1 Integration Strategies

Integrating with third-party APIs requires proper error handling, retries, and rate limiting.

// Third-party API integration
const axios = require('axios');

class ThirdPartyAPI {
    constructor(apiKey) {
        this.client = axios.create({
            baseURL: 'https://api.thirdparty.com',
            headers: { 'Authorization': `Bearer ${apiKey}` },
            timeout: 5000
        });
    }
    
    async getData(id, retries = 3) {
        for (let i = 0; i < retries; i++) {
            try {
                const response = await this.client.get(`/data/${id}`);
                return response.data;
            } catch (error) {
                if (i === retries - 1) throw error;
                await this.delay(1000 * (i + 1)); // Exponential backoff
            }
        }
    }
    
    delay(ms) {
        return new Promise(resolve => setTimeout(resolve, ms));
    }
}

13.2 Webhook Implementation

// Receiving webhooks
app.post('/webhooks/payment', async (req, res) => {
    const signature = req.headers['x-signature'];
    const isValid = verifySignature(req.body, signature);
    
    if (!isValid) {
        return res.status(401).send('Invalid signature');
    }
    
    // Process webhook
    await processPaymentWebhook(req.body);
    
    res.status(200).send('OK');
});

// Sending webhooks
async function sendWebhook(url, payload) {
    try {
        await axios.post(url, payload, {
            headers: { 'Content-Type': 'application/json' },
            timeout: 5000
        });
    } catch (error) {
        // Retry logic
        console.error('Webhook failed:', error);
    }
}

13.3 API Gateway Pattern

// Aggregate multiple API calls
app.get('/api/user-dashboard/:userId', async (req, res) => {
    const { userId } = req.params;
    
    const [user, orders, notifications] = await Promise.all([
        userService.getUser(userId),
        orderService.getUserOrders(userId),
        notificationService.getUserNotifications(userId)
    ]);
    
    res.json({ user, orders, notifications });
});