redis-sliding-rate-limiter/src/strategies/RedisStrategy.ts

Flexible and performant rate limiter based on sliding window algorithm with arbitrary precision

import { Strategy } from './Strategy';
import { RateLimiterResponse } from '../RateLimiter';
import {
    LuaScript,
    MicrosecondsToWindowSubdivision,
} from '../lua';

export class RedisStrategy extends Strategy {
    async sendCommand(cmd: string, ...args: any[]): Promise<any> {
        return await this.limiter.client.sendCommand!([cmd, ...args]);
    }

    async loadScript(): Promise<string> {
        return await this.sendCommand('SCRIPT', 'LOAD', LuaScript);
    }

    async execScript(key: any): Promise<RateLimiterResponse> {
        if (!this.scriptSha1) {
            this.scriptSha1 = await this.loadScript();
        }

        // NB: redis library sendCommand function accepts arguments only as string or Buffer
        const args = [
            this.scriptSha1,
            '1', // number of keys
            `${key}`,
            `${this.limiter.window}`,
            `${MicrosecondsToWindowSubdivision[this.limiter.windowSubdivisionUnit]}`,
            `${this.limiter.windowExpireMs}`,
            `${this.limiter.limit}`,
            `${this.limiter.limitOverhead}`
        ];

        let res: any;

        try {
            res = await this.sendCommand('EVALSHA', ...args);
        }
        catch(err: any) {
            // Script expired in Redis cache, reload and try again
            if (err && err.message && err.message.includes('NOSCRIPT')) {
                this.scriptSha1 = await this.loadScript();
                args[0] = this.scriptSha1;
                res = await this.sendCommand('EVALSHA', ...args);
            }
            else {
                throw err;
            }
        }

        return {
            allowed: !!res[0],
            remaining: Math.max(0, res[1]),
            firstExpireAtMs: res[2],
            windowExpireAtMs: res[3]
        };
    }
}