pr-monitor/server/sse.ts

import type { Response } from 'express';
import type { SyncEventPayload } from '../shared/types.js';

const clients = new Set<Response>();

export function addClient(res: Response, initial: SyncEventPayload): void {
  res.writeHead(200, {
    'content-type': 'text/event-stream',
    'cache-control': 'no-cache',
    connection: 'keep-alive',
    'x-accel-buffering': 'no',
  });
  res.write('retry: 3000\n\n');
  res.write(frame(initial));
  clients.add(res);
  res.on('close', () => clients.delete(res));
}

export function broadcast(payload: SyncEventPayload): void {
  const data = frame(payload);
  for (const res of clients) res.write(data);
}

function frame(payload: SyncEventPayload): string {
  return `event: sync\ndata: ${JSON.stringify(payload)}\n\n`;
}

setInterval(() => {
  for (const res of clients) res.write(': ping\n\n');
}, 25_000).unref();