Implement Rate Limiting for APIs

Here's a production-ready sliding window rate limiter implementation for FastAPI with Redis: ```python import time import json from typing import Optional from fastapi import HTTPException, Request from redis import Redis import logging class SlidingWindowRateLimiter: def __init__(self, redis_client: Redis, default_limit: int = 100, window_size: int = 60): self.redis = redis_client self.default_limit = default_limit self.window_size = window_size self.logger = logging.getLogger(__name__) async def is_allowed(self, identifier: str, limit: Optional[int] = None) -> tuple[bool, dict]: limit = limit or self.default_limit now = time.time() pipeline = self.redis.pipeline() # Remove expired entries pipeline.zremrangebyscore(identifier, 0, now - self.window_size) # Count current requests pipeline.zcard(identifier) # Add current request pipeline.zadd(identifier, {str(now): now}) # Set expiration pipeline.expire(identifier, self.window_size + 1) results = pipeline.execute() current_requests = results[1] remaining = max(0, limit - current_requests) reset_time = int(now + self.window_size) headers = { 'X-RateLimit-Limit': str(limit), 'X-RateLimit-Remaining': str(remaining), 'X-RateLimit-Reset': str(reset_time) } if current_requests >= limit: # Remove the request we just added since it's rejected self.redis.zrem(identifier, str(now)) return False, headers return True, headers def rate_limit(requests_per_minute: int = 100): def decorator(func): async def wrapper(request: Request, *args, **kwargs): # Extract identifier (IP, user_id, or API key) identifier = get_client_identifier(request) allowed, headers = await rate_limiter.is_allowed( identifier, requests_per_minute ) if not allowed: raise HTTPException( status_code=429, detail="Rate limit exceeded. Please try again later.", headers=headers ) response = await func(request, *args, **kwargs) # Add rate limit headers to successful responses for key, value in headers.items(): response.headers[key] = value return response return wrapper return decorator ``` This implementation provides sliding window rate limiting with Redis persistence, proper HTTP headers, and easy FastAPI integration.