def stream(request):
    last_id = int(request.headers.get("Last-Event-ID", "0"))
    for evt in fetch_events_since(last_id):
        yield f"id: {evt.id}\nevent: {evt.type}\ndata: {evt.json()}\n\n"

import requests

# parse_until_count(r, n): read the stream until n complete events parse, return them
def test_replay_via_last_event_id():
    # First connection - read 5 events, then close
    with requests.get("http://localhost:8080/stream", stream=True) as r:
        events = parse_until_count(r, 5)
        last_id = events[-1]["id"]

    # Reconnect with Last-Event-ID
    headers = {"Last-Event-ID": last_id}
    with requests.get("http://localhost:8080/stream", stream=True, headers=headers) as r:
        replay = parse_until_count(r, 1)
        assert int(replay[0]["id"]) > int(last_id)

retry: 10000

test('client honors retry: 10000 on disconnect', async ({ page }) => {
  // Server emits retry: 10000, then closes
  const reconnectMs = await page.evaluate(() => {
    return new Promise<number>((resolve) => {
      const es = new EventSource('/api/stream-with-retry');
      let openTime = 0;
      es.onopen = () => {
        if (openTime === 0) {
          openTime = performance.now();
        } else {
          es.close();
          resolve(performance.now() - openTime);
        }
      };
    });
  });
  // Allow +/-20% slack
  expect(reconnectMs).toBeGreaterThanOrEqual(8000);
  expect(reconnectMs).toBeLessThanOrEqual(12000);
});

def stream(request):
    if user_unsubscribed(request):
        return Response(status=204)
    # ... event stream ...

test('client stops reconnecting after server returns 204', async ({ page }) => {
  // Server returns 204 immediately
  const states = await page.evaluate(() => {
    return new Promise<number[]>((resolve) => {
      const es = new EventSource('/api/stream-204');
      const seen: number[] = [];
      const interval = setInterval(() => seen.push(es.readyState), 100);
      setTimeout(() => {
        clearInterval(interval);
        resolve(seen);
      }, 2000);
    });
  });
  expect(states[states.length - 1]).toBe(2); // CLOSED
});

test('app uses single EventSource for fan-out', async ({ page }) => {
  await page.goto('https://localhost:3000/dashboard');

  const eventSourceCount = await page.evaluate(() =>
    performance.getEntriesByType('resource')
      .filter((r) => r.name.includes('/api/stream'))
      .length
  );
  expect(eventSourceCount).toBe(1);
});