WebSockets vs Long Polling: From Legacy to Real-Time

Quick Summary

Long polling was the original hack for real-time web communication before WebSockets existed. While it simulates real-time updates through clever use of HTTP requests, WebSockets provide true bidirectional, persistent connections with significantly better performance and resource efficiency. Today, long polling primarily serves as a fallback mechanism for environments where WebSockets aren’t available.

At a Glance Comparison

Feature	Long Polling	WebSockets
Connection Type	HTTP Request/Response cycles	Persistent TCP connection
Direction	Client-initiated only	True bidirectional
Real-time	Simulated (polling delays)	Native real-time
Protocol Overhead	High (HTTP headers each request)	Low (after handshake)
Server Resources	High (connection churn)	Efficient (persistent)
Client Battery	High drain (constant requests)	Low drain
Firewall Friendly	✅ Yes (standard HTTP)	Usually (port 80/443)
Proxy Support	✅ Excellent	Good with modern proxies
Browser Support	100%	99%+
Complexity	Medium	Low-Medium
Message Ordering	Can be problematic	Guaranteed
Connection State	Stateless	Stateful

How Long Polling Works

Long polling extends the traditional request-response model by holding HTTP connections open until the server has data to send:

Client makes request: Opens standard HTTP connection
Server holds connection: Doesn’t respond immediately
Event occurs: Server sends response with data
Client reconnects: Immediately opens new request
Cycle repeats: Creates illusion of real-time

The Long Polling Lifecycle

// Client-side long polling implementation
class LongPoller {
  constructor(url) {
    this.url = url;
    this.polling = false;
  }

  async start() {
    this.polling = true;
    while (this.polling) {
      try {
        // Make request and wait for response
        const response = await fetch(this.url, {
          method: 'GET',
          // Long timeout to hold connection
          signal: AbortSignal.timeout(30000)
        });

        if (response.ok) {
          const data = await response.json();
          this.onMessage(data);
        }
      } catch (error) {
        if (error.name === 'AbortError') {
          // Timeout is normal, just reconnect
        } else {
          // Real error, wait before retry
          await this.delay(1000);
        }
      }
      // Immediately reconnect for next message
    }
  }

  stop() {
    this.polling = false;
  }

  delay(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
  }

  onMessage(data) {
    console.log('Received:', data);
  }
}

const express = require('express');
const app = express();

// Store pending requests
const pendingRequests = new Map();

app.get('/poll', (req, res) => {
  const clientId = req.query.clientId || generateId();

  // Store response object to send data later
  pendingRequests.set(clientId, res);

  // Set timeout to prevent infinite hanging
  const timeout = setTimeout(() => {
    if (pendingRequests.has(clientId)) {
      res.json({ type: 'timeout' });
      pendingRequests.delete(clientId);
    }
  }, 30000);

  // Clean up on client disconnect
  req.on('close', () => {
    clearTimeout(timeout);
    pendingRequests.delete(clientId);
  });
});

// When event occurs, notify waiting clients
function broadcastMessage(message) {
  pendingRequests.forEach((res, clientId) => {
    res.json({ type: 'message', data: message });
    pendingRequests.delete(clientId);
  });
}

from flask import Flask, request, jsonify
import time
import threading

app = Flask(__name__)
pending_requests = {}
messages_queue = []

@app.route('/poll')
def long_poll():
    client_id = request.args.get('clientId', generate_id())
    timeout = 30  # seconds

    start_time = time.time()

    # Wait for message or timeout
    while time.time() - start_time < timeout:
        if messages_queue:
            message = messages_queue.pop(0)
            return jsonify({'type': 'message', 'data': message})
        time.sleep(0.1)  # Small delay to prevent CPU spinning

    # Timeout reached
    return jsonify({'type': 'timeout'})

def broadcast_message(message):
    messages_queue.append(message)

How WebSockets Work

WebSockets establish a persistent, full-duplex connection through an HTTP upgrade:

// Client-side WebSocket - Simple and efficient
const ws = new WebSocket('wss://example.com/socket');

ws.onopen = () => {
  console.log('Connected once');
  ws.send('Hello Server');
};

ws.onmessage = (event) => {
  console.log('Received:', event.data);
  // Server can push at any time
};

ws.onerror = (error) => {
  console.error('WebSocket error:', error);
};

ws.onclose = () => {
  console.log('Disconnected');
  // Implement reconnection logic
};

// Send multiple messages over same connection
ws.send('Message 1');
ws.send('Message 2');
// No HTTP overhead, just frame headers

Key Differences

Connection Management

Long Polling: Constant connection cycling

New TCP connection for each poll
TCP handshake overhead repeated
Connection state lost between requests
Session management complexity

WebSockets: Single persistent connection

One TCP connection maintained
Handshake happens once
Stateful connection
Simple session tracking

Message Delivery Timing

Long Polling: Potential delays

Message arrives while client reconnecting = delay
Timeout cycles can miss messages
Race conditions possible
Ordering issues with concurrent requests

WebSockets: Immediate delivery

Messages pushed instantly
No reconnection gaps
Guaranteed message ordering
No timing issues

Resource Usage

Long Polling creates significant overhead:

Each poll cycle requires new HTTP headers (500-2000 bytes)
Server must handle connection churn
Client CPU usage for constant reconnection
Network overhead for TCP handshakes

WebSockets are efficient:

Minimal frame overhead (2-14 bytes)
Single connection to maintain
Lower CPU usage on both ends
Reduced network traffic

Implementation Complexity

Long Polling requires handling:

Reconnection logic
Timeout management
Message queueing
Duplicate detection
Connection tracking
Error recovery

WebSockets simplify development:

Built-in connection management
Native browser API
Straightforward error handling
Simple message passing
Library ecosystem mature

Use Case Analysis

When Long Polling Might Still Apply

✅ Restricted environments:

Corporate firewalls blocking WebSocket
Legacy proxy servers
Environments with WebSocket issues

✅ Simple notification systems:

Infrequent updates
One-way server notifications
Fallback mechanism

✅ Compatibility requirements:

Supporting ancient browsers
Maximum compatibility needed
Simple HTTP-only infrastructure

When WebSockets Excel

✅ Real-time applications:

Chat and messaging
Live collaboration
Gaming and interactive apps
Financial trading platforms
Live sports updates
IoT data streams

✅ High-frequency updates:

Monitoring dashboards
Real-time analytics
Location tracking
Sensor data
Live feeds

✅ Bidirectional communication:

Interactive features
User presence
Collaborative editing
Remote control
Video/audio signaling

Implementation Examples

Fallback Pattern: WebSocket with Long Polling Fallback

class RealTimeConnection {
  constructor(wsUrl, pollUrl) {
    this.wsUrl = wsUrl;
    this.pollUrl = pollUrl;
    this.useWebSocket = this.supportsWebSocket();
  }

  supportsWebSocket() {
    return 'WebSocket' in window &&
           window.WebSocket.CLOSING === 2;
  }

  connect() {
    if (this.useWebSocket) {
      this.connectWebSocket();
    } else {
      console.log('WebSocket not available, using long polling');
      this.startLongPolling();
    }
  }

  connectWebSocket() {
    this.ws = new WebSocket(this.wsUrl);

    this.ws.onopen = () => {
      console.log('WebSocket connected');
      this.onConnect();
    };

    this.ws.onmessage = (event) => {
      this.onMessage(JSON.parse(event.data));
    };

    this.ws.onerror = () => {
      // Could fall back to polling here
      console.log('WebSocket error, attempting reconnect');
      setTimeout(() => this.connectWebSocket(), 1000);
    };
  }

  startLongPolling() {
    this.polling = true;
    this.poll();
  }

  async poll() {
    while (this.polling) {
      try {
        const response = await fetch(this.pollUrl);
        const data = await response.json();

        if (data.type !== 'timeout') {
          this.onMessage(data);
        }
      } catch (error) {
        await this.delay(1000);
      }
    }
  }

  send(message) {
    if (this.ws && this.ws.readyState === WebSocket.OPEN) {
      this.ws.send(JSON.stringify(message));
    } else {
      // For polling, need separate endpoint
      fetch(this.pollUrl, {
        method: 'POST',
        body: JSON.stringify(message)
      });
    }
  }

  onConnect() {
    console.log('Connected');
  }

  onMessage(data) {
    console.log('Message received:', data);
  }

  delay(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
  }
}

// Usage
const connection = new RealTimeConnection(
  'wss://api.example.com/socket',
  'https://api.example.com/poll'
);
connection.connect();

The Evolution: Why WebSockets Won

Historical Context

Long polling emerged in the early 2000s as a clever workaround for the web’s request-response limitations. Technologies like Comet, BOSH, and Bayeux all used variations of long polling to simulate real-time communication.

WebSockets, standardized in 2011, provided what developers actually needed: a proper bidirectional communication protocol designed for real-time from the ground up.

Technical Advantages of WebSockets

Protocol Efficiency: Purpose-built for real-time communication
Native Browser Support: No hacks or workarounds needed
Standardized: RFC 6455 provides clear implementation guidelines
Ecosystem: Mature libraries and tools available
Performance: Lower latency, less overhead, better scaling

Modern Reality

Today, WebSockets are supported by 99%+ of browsers and all major server platforms. The reasons to use long polling have largely disappeared except for specific edge cases or as a fallback mechanism.

Working with WebSocket Providers

While raw WebSocket implementation is straightforward, production deployments benefit from using established protocols and services:

Open Source Solutions like Socket.IO provide:

Automatic fallback to long polling
Reconnection handling
Room/namespace abstractions
Built-in message acknowledgments

Commercial Services like Ably offer:

Global infrastructure
Automatic scaling
Connection state recovery
Message ordering guarantees
Multiple protocol support

These solutions abstract away the complexities of managing WebSocket infrastructure while providing robust handling of edge cases and failure scenarios. For most applications, using a WebSocket-based service or library is recommended over implementing raw WebSocket protocols.

Conclusion

Long polling served its purpose in the evolution of real-time web technologies, but WebSockets have definitively superseded it for modern applications. The efficiency, simplicity, and performance benefits of WebSockets make them the clear choice for real-time communication.

Key Takeaways:

WebSockets are superior for real-time communication in almost every metric
Long polling is legacy technology, useful mainly as a fallback
Modern browsers have excellent WebSocket support (99%+)
Using WebSocket providers simplifies implementation and improves reliability
The complexity of long polling isn’t worth it for new projects

For new projects requiring real-time features, WebSockets should be your default choice. The ecosystem is mature, support is universal, and the performance benefits are significant.