server/sse.ts

import type {Response} from 'express';

export function initSse(res: Response): void {
  res.setHeader('Content-Type', 'text/event-stream');
  res.setHeader('Cache-Control', 'no-cache');
  res.setHeader('Connection', 'keep-alive');
  res.flushHeaders?.();
}

export function writeSse(res: Response, event: string, data: unknown): void {
  res.write(`event: ${event}\n`);
  res.write(`data: ${JSON.stringify(data)}\n\n`);
}

export function writeSseComment(res: Response, comment: string): void {
  res.write(`: ${comment}\n\n`);
}