Implementing Redis-Based Rate Limiting in PHP

This article addresses the practical problem of implementing rate limiting for orders using Redis, allowing a configurable number of accesses per defined time interval.

It provides a PHP function isAllow that determines whether a request should be permitted based on a Redis key that incorporates the current timestamp modulo the interval, incrementing the counter atomically and setting an expiration.

<?php
/**
 * 是否允许放行
 * @param string $key       redis键前缀
 * @param int $timeInterval 时间间隔（秒）
 * @param int $max          时间间隔内最大放行数
 * @return bool             是否放行
 * @throws Exception
 * @example
 * //每秒放行一个
 * isAllow('my_allow');
 *
 * //每秒放行3个
 * isAllow('my_allow',1,3);
 *
 * //每3秒放行2个
 * isAllow('my_allow',3,2);
 */
function isAllow(string $key, int $timeInterval=1, int $max=1):bool{
    if($timeInterval<1){
        throw new Exception('时间间隔必须大于0');
    }
    if($max<1){
        throw new Exception('最大放行数必须大于0');
    }
    $redis = new Redis();
    $redis->connect('192.168.31.187');
    if(!$redis->isConnected()){
        throw new Exception('Redis服务连接失败');
    }
    //对时间戳取模，使得每$timeInterval秒取得同一个时间戳
    $time = time();
    $key .= ':' . ($time - ($time % $timeInterval));
    //自增并返回自增后的结果
    $index = $redis->incr($key);
    //如果是第一个访问，设置键的过期时间
    if($index === 1){
        $redis->expire($key, $timeInterval + 1);
    }
    return $index < $max + 1;
}
?>

The accompanying explanation highlights four key points: the timestamp modulo creates a key that refreshes every interval; incr() atomically increments the counter, creating the key if absent; the returned value indicates the request order; and the key expires shortly after the interval, ensuring it does not persist.

Readers are invited to ask questions, suggest corrections, or propose optimizations.