@fanoutio/eventstream/build/stream/ServerSentEventsSerializer.js

Connect-compatible middleware that enables the easy creation of EventStream endpoints

import { Transform } from 'stream';
import { encodeEvent } from '../utils/textEventStream.js';
import { KEEP_ALIVE_TIMEOUT } from '../constants.js';
export default class ServerSentEventsSerializer extends Transform {
    keepAliveTimer;
    constructor() {
        super({ writableObjectMode: true });
        this.keepAliveTimer = null;
        this.setupKeepAliveTimer();
    }
    _transform(event, _encoding, callback) {
        try {
            this.setupKeepAliveTimer();
            const encodedEvent = encodeEvent({
                event: event.event,
                data: JSON.stringify(event.data),
            });
            this.push(encodedEvent);
        }
        catch (ex) {
            const err = ex instanceof Error ? ex : new Error(String(ex));
            callback(err);
            return;
        }
        callback();
    }
    setupKeepAliveTimer() {
        if (this.keepAliveTimer != null) {
            clearInterval(this.keepAliveTimer);
            this.keepAliveTimer = null;
        }
        this.keepAliveTimer = setInterval(() => {
            const encodedEvent = encodeEvent({
                event: 'keep-alive',
                data: '',
            });
            this.push(encodedEvent);
        }, KEEP_ALIVE_TIMEOUT * 1000);
    }
}