swaf/src/Throttler.ts

import {TooManyRequestsHttpError} from "./HttpError";

export default class Throttler {
    private static readonly throttles: { [throttleName: string]: Throttle } = {};

    /**
     * Throttle function; will throw a TooManyRequestsHttpError when the threshold is reached.
     *
     * This throttle is adaptive: it will slowly decrease (linear) until it reaches 0 after {@param resetPeriod} ms.
     * Threshold will hold for {@param holdPeriod} ms.
     *
     * @param action a unique action name (can be used multiple times, but it'll account for a single action).
     * @param max how many times this action can be triggered per id.
     * @param resetPeriod after how much time in ms the throttle will reach 0.
     * @param id an identifier of who triggered the action.
     * @param holdPeriod time in ms after each call before the threshold begins to decrease.
     * @param jailPeriod time in ms for which the throttle will throw when it is triggered.
     */
    public static throttle(action: string, max: number, resetPeriod: number, id: string, holdPeriod: number = 100, jailPeriod: number = 30 * 1000) {
        let throttle = this.throttles[action];
        if (!throttle) throttle = this.throttles[action] = new Throttle(max, resetPeriod, holdPeriod, jailPeriod);
        throttle.trigger(id);
    }

    private constructor() {
    }
}

class Throttle {
    private readonly max: number;
    private readonly resetPeriod: number;
    private readonly holdPeriod: number;
    private readonly jailPeriod: number;
    private readonly triggers: {
        [id: string]: {
            count: number,
            lastTrigger?: number,
            jailed?: number;
        }
    } = {};

    constructor(max: number, resetPeriod: number, holdPeriod: number, jailPeriod: number) {
        this.max = max;
        this.resetPeriod = resetPeriod;
        this.holdPeriod = holdPeriod;
        this.jailPeriod = jailPeriod;
    }


    public trigger(id: string) {
        let trigger = this.triggers[id];
        if (!trigger) trigger = this.triggers[id] = {count: 0};

        let currentDate = new Date().getTime();

        if (trigger.jailed && currentDate - trigger.jailed < this.jailPeriod) {
            this.throw();
            return;
        }

        if (trigger.lastTrigger) {
            let timeDiff = currentDate - trigger.lastTrigger;
            if (timeDiff > this.holdPeriod) {
                timeDiff -= this.holdPeriod;
                trigger.count = Math.floor(Math.min(trigger.count, this.max * (1 - timeDiff / this.resetPeriod)));
            }
        }

        trigger.count++;
        trigger.lastTrigger = currentDate;

        if (trigger.count > this.max) {
            trigger.jailed = currentDate;
            this.throw();
            return;
        }
    }

    private throw() {
        throw new TooManyRequestsHttpError();
    }
}