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Real-Time Communication on the Web: Long Polling vs SSE vs WebSockets vs QUIC

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📑 Table of Contents

  1. Introduction
  2. The Evolution of Real-Time Communication
  3. Long Polling
  • What is Long Polling?
  • How it works (Diagram)
  • Pros and Cons
  • Use Cases

  • Example (Node.js or Python snippet)

    1. Server-Sent Events (SSE)

  • What is SSE?

  • How it works (Diagram)

  • Browser and Server Support

  • Pros and Cons

  • Use Cases

  • Example (Spring Boot / Express.js)

    1. WebSockets

  • What are WebSockets?

  • Full Duplex vs Half Duplex

  • How it works (Handshake, Frames) + Diagram

  • Pros and Cons

  • Use Cases

  • Example (Socket.IO, Spring WebSocket)

    1. QUIC (HTTP/3)

  • What is QUIC?

  • Why it was created (limitations of TCP)

  • How it works (UDP + TLS + multiplexing)

  • Pros and Cons

  • Use Cases

  • Example (gRPC over QUIC)

    1. Comparison Table: Long Polling vs SSE vs WebSockets vs QUIC
    2. Decision Guide: When to Use What

  • By Use Case (e.g., chat, stock updates, video streaming, telemetry)

  • By Infrastructure Constraints (e.g., firewall, mobile network)

  • By Protocol Support (e.g., browser support, proxies, HTTP/2/3)

    1. Real-World Use Cases by Tech Companies

  • Facebook: Long Polling (historically)

  • Twitter: SSE for streaming tweets

  • Slack: WebSockets for messaging

  • Google Meet / Zoom: QUIC for real-time audio/video

    1. Performance & Scalability Considerations
    2. Bandwidth Usage
    3. Server Resource Utilization
    4. Message Latency
    5. Connection Limits
    6. Security Implications
    7. CORS
    8. TLS/SSL
    9. DDoS Risks
    10. Future Trends
    11. HTTP/3 Adoption
    12. WebTransport (QUIC-based successor to WebSockets)
    13. Conclusion
    14. TL;DR Summary
    15. Decision Flowchart
    16. Resources and Further Reading

📘 Example Code Snippets to Include

  • Long Polling (Node.js/Express): 
  app.get('/poll', (req, res) => {
    setTimeout(() => {
      res.json({ data: 'new data' });
    }, 10000); // Simulating delay
  });
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  • SSE (Express or Spring): 
  res.setHeader('Content-Type', 'text/event-stream');
  res.write(`data: ${JSON.stringify({ message: 'Hello SSE' })}\n\n`);
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  • WebSocket (Socket.IO): 
  io.on('connection', socket => {
    socket.emit('message', 'Welcome!');
  });
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  • QUIC (gRPC over HTTP/3 using Go): 
  grpc.NewServer(grpc.Creds(credentials.NewTLS(quicTLSConfig)))
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📊 Comparison Table Example

Feature Long Polling SSE WebSocket QUIC
Protocol HTTP HTTP WS over TCP HTTP/3 (QUIC)
Duplex Half Server → Client Full Full
Connection Overhead High Low Low Very Low
Browser Support ✅ ✅ (No IE) ✅ 🚧 Limited
Best Use Case Legacy support Live feeds Real-time chat Video streaming
Firewall Friendly ✅ ✅ ❌ (Sometimes) ✅

✅ Use Case Guide

Use Case Best Option Why?
Chat App WebSocket Bi-directional, low latency
Stock Market Updates SSE One-way, lightweight, built on HTTP
IoT Device Telemetry QUIC or WebSocket Efficient multiplexing and low latency
Video Streaming QUIC UDP-based, optimized for media
News Feed (Fallback) Long Polling Works everywhere, even with HTTP/1.1

📚 References

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