Bits of .NET

📡 One-Way Real-Time Updates

Need live updates but not bidirectional? EventSource (SSE) is simpler than WebSockets. Auto-reconnects. Built-in retry. Perfect for dashboards, notifications.

📝 Client-Side

const eventSource = new EventSource('/api/events');

// Listen for messages
eventSource.onmessage = (event) => {
  const data = JSON.parse(event.data);
  console.log('Update:', data);
  updateUI(data);
};

// Listen for specific event type
eventSource.addEventListener('notification', (event) => {
  const notification = JSON.parse(event.data);
  showNotification(notification);
});

// Error handling (auto-reconnect)
eventSource.onerror = (error) => {
  console.error('SSE error:', error);
  // EventSource automatically tries to reconnect
};

// Close when done
// eventSource.close();

🎯 Server-Side (Node.js)

app.get('/api/events', (req, res) => {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive',
    'Access-Control-Allow-Origin': '*'
  });
  
  // Send message every 5 seconds
  const interval = setInterval(() => {
    const data = { time: new Date().toISOString(), value: Math.random() };
    res.write(`data: ${JSON.stringify(data)}\n\n`);
  }, 5000);
  
  // Send notification event
  setTimeout(() => {
    res.write(`event: notification\n`);
    res.write(`data: ${JSON.stringify({ message: 'Welcome!' })}\n\n`);
  }, 1000);
  
  req.on('close', () => clearInterval(interval));
});

✅ Use Cases

• Live sports scores, stock tickers
• Real-time dashboards (CPU, memory)
• Notification feeds
• Progress updates (file upload, batch processing)
• Social media feeds (one-way)

💡 SSE vs WebSockets

• SSE: One-way (server → client), HTTP, auto-reconnect, simpler
• WebSockets: Two-way, requires upgrade, more complex
• SSE has built-in retry and reconnection
• SSE can’t send from client to server (use fetch for that)
• Maximum 6 connections per domain (HTTP/1.1)