kannon-client/classes/Heartbeat.js

const EventEmitter = require('events');
const Message = require('./Message.js');

class Heartbeat extends EventEmitter {

    constructor(eventParser) {
        super();
        this.interval = config?.server?.heartbeat || 10000;
        this.eventParser = eventParser;
        this.#listenForPingPong();
        this.#sendPing();
    }   

    async #sendPing() {
        if (this.timeout !== undefined) {
            clearTimeout(this.timeout);
        }
        if (this.alive === false) {
            this.emit('timeout');
            return;
        } else if (this.alive === undefined) {
            await new Promise((resolve, reject) => {
                setTimeout(resolve, this.interval);
            })
        }
        this.alive = false;
        await new Message('ping').send();
        this.timeout = setTimeout(() => {
            this.#sendPing();
        },  this.interval);
    }

    async #listenForPingPong() {
        this.eventParser.on('ping', () => {
            logger.debug('handling event \'ping\', responding with \'pong\'...');
            new Message('pong').send();
        });
        this.eventParser.on('pong', () => {
            logger.debug('handling event \'pong\'...');
            this.alive = true;
        });
    }

    destroy() {
        if (this.timeout !== undefined) {
            clearTimeout(this.timeout);
        }
        this.eventParser.removeAllListeners('ping');
        this.eventParser.removeAllListeners('pong');
    }

}

module.exports = Heartbeat;