feat: Implement the core InterNetX DDNS updater application with API, services, middleware, Docker support, and a detailed README.

src/middleware/rateLimiter.middleware.js

@@ -0,0 +1,50 @@
+const rateLimit = require('express-rate-limit');
+const config = require('../config/config');
+const { logger } = require('../utils/logger');
+
+/**
+ * Rate limiter for update endpoint
+ */
+const updateLimiter = rateLimit({
+    windowMs: config.rateLimit.windowMs,
+    max: config.rateLimit.maxRequests,
+
+    message: {
+        error: 'Too many requests',
+        message: 'Rate limit exceeded. Please try again later.',
+    },
+
+    standardHeaders: true, // Return rate limit info in `RateLimit-*` headers
+    legacyHeaders: false, // Disable `X-RateLimit-*` headers
+
+    // Custom handler for rate limit exceeded
+    handler: (req, res) => {
+        logger.warn('Rate limit exceeded', {
+            ip: req.ip,
+            path: req.path,
+            limit: config.rateLimit.maxRequests,
+            window: `${config.rateLimit.windowMs / 1000}s`,
+        });
+
+        res.status(429).json({
+            error: 'Too many requests',
+            message: 'You have exceeded the rate limit. Please try again later.',
+            retryAfter: Math.ceil(config.rateLimit.windowMs / 1000),
+        });
+    },
+
+    // Skip rate limiting for successful requests (optional)
+    skip: (req) => {
+        // Could skip based on certain conditions, e.g., whitelisted IPs
+        return false;
+    },
+
+    // Key generator - rate limit per IP
+    keyGenerator: (req) => {
+        return req.ip;
+    },
+});
+
+module.exports = {
+    updateLimiter,
+};