Rate Limiter with Sliding Window

javascript Copy Code

class SlidingWindowRateLimiter {
    constructor({ windowMs = 60000, maxRequests = 100 } = {}) {
        this.windowMs = windowMs;
        this.maxRequests = maxRequests;
        this.clients = new Map();

        // Cleanup expired entries every minute
        setInterval(() => this.cleanup(), 60000);
    }

    cleanup() {
        const now = Date.now();
        for (const [key, timestamps] of this.clients) {
            const valid = timestamps.filter(t => now - t < this.windowMs);
            if (valid.length === 0) this.clients.delete(key);
            else this.clients.set(key, valid);
        }
    }

    isAllowed(key) {
        const now = Date.now();
        const timestamps = this.clients.get(key) || [];
        const valid = timestamps.filter(t => now - t < this.windowMs);
        valid.push(now);
        this.clients.set(key, valid);
        return {
            allowed: valid.length <= this.maxRequests,
            remaining: Math.max(0, this.maxRequests - valid.length),
            resetMs: valid.length > 0 ? this.windowMs - (now - valid[0]) : 0
        };
    }

    middleware() {
        return (req, res, next) => {
            const key = req.ip || req.connection.remoteAddress;
            const { allowed, remaining, resetMs } = this.isAllowed(key);
            res.setHeader('X-RateLimit-Limit', this.maxRequests);
            res.setHeader('X-RateLimit-Remaining', remaining);
            if (!allowed) {
                return res.status(429).json({
                    error: 'Too many requests',
                    retryAfter: Math.ceil(resetMs / 1000)
                });
            }
            next();
        };
    }
}

module.exports = SlidingWindowRateLimiter;

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