Server-Sent Events over HTTP/2 on Node.JS

gistfile1.txt

Relays messages published on a redis channel over Server-Sent Events.

sse.http2.ts

import redis from 'redis';
import { readFileSync } from 'node:fs';
import { createSecureServer } from 'node:http2';
import EventEmitter from 'node:events';

const server = createSecureServer(
  {
    key: readFileSync('localhost-key.pem'),
    cert: readFileSync('localhost.pem'),
    allowHTTP1: true
  },
  (req, res) => {
    if (req.httpVersionMajor !== 2) {
      res.statusCode = 400;
      res.end("HTTP/2 only");
    }
  }
);
server.on('error', (err) => console.error(err));

const sseMessage = Symbol('SSE Message');
const sseEvents = new EventEmitter();

const client = redis.createClient({ url: 'redis://localhost:6379' });
await client.connect();
await client.subscribe('chat', (message) => {
  sseEvents.emit(sseMessage, message);
});

server.on('stream', (stream, headers) => {
  if (headers[':path'] !== '/sse') return;
  if (headers[':method'] !== 'GET') return;
  stream.respond({
    ':status': 200,
    'content-type': 'text/event-stream',
    'cache-control': 'no-cache',
  });
  const onMessage = (message: string) => stream.write(`data: ${message}\n\n`);
  sseEvents.on(sseMessage, onMessage);
  stream.on('close', () => sseEvents.off(sseMessage, onMessage));
});

server.on("stream", (stream) => {
  if (stream.headersSent) return;
  stream.respond({ ":status": 404 });
  stream.end("not found");
});

server.listen(8443);