Nodejs-Webserver – Server and Clients

🔷 Introduction to Web Servers

A web server is a system that:

• Accepts requests from clients (usually web browsers),
• Processes those requests, and
• Sends back a response (such as HTML, JSON, or files).

In Node.js, we can create a web server using the built-in http module without any external dependencies.

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🧠 Key Concepts

Term	Description
Server	A machine or application that provides services/data to the clients
Client	The user or software (like a browser) that sends a request to the server
HTTP	Protocol used for communication between client and server
Request	Message sent by the client asking for data or action
Response	Message sent back from server with data/status based on the request

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🔧 How Node.js Creates a Web Server?

Node.js has a built-in module called http that allows you to create a web server without any external tools.

✅ Basic Example:

const http = require('http');

// Create server
const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' }); // Set response header
  res.end('Hello, MCA Students! Welcome to Node.js Web Server.');
});

// Server listens on port 3000
server.listen(3000, () => {
  console.log('Server running at http://localhost:3000/');
});

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🔁 Client-Server Communication Flow (Diagram Representation)

   [Client (Browser)]
        |
        |   HTTP Request (GET /index.html)
        ↓
   [Node.js Web Server]
        |
        |   Processes the request
        |   Reads file / prepares data
        ↓
   [Sends Response] → HTTP 200 OK, HTML or JSON Content
        ↓
   [Client (renders result)]

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🔄 Handling Different Client Requests

Node.js can handle different routes based on the URL using conditional checks.

📄 Example:

const http = require('http');

const server = http.createServer((req, res) => {
  if (req.url === '/') {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end('<h1>Welcome to Home Page</h1>');
  } else if (req.url === '/about') {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end('<h1>About Us</h1>');
  } else {
    res.writeHead(404, {'Content-Type': 'text/html'});
    res.end('<h1>404 Not Found</h1>');
  }
});

server.listen(3000, () => {
  console.log("Server running at http://localhost:3000/");
});

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🧰 Serving HTML, JSON, and Files

📄 Serve JSON:

if (req.url === '/api') {
  const data = { name: "MCA Student", course: "Node.js" };
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify(data));
}

📁 Serve a file (HTML page):

const fs = require('fs');
if (req.url === '/home') {
  fs.readFile('home.html', (err, data) => {
    if (err) {
      res.writeHead(500);
      res.end('Error loading file');
    } else {
      res.writeHead(200, {'Content-Type': 'text/html'});
      res.end(data);
    }
  });
}

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⚙️ Role of Ports in Server Communication

• A port is a logical endpoint for communication.
• When you run server.listen(3000), you’re saying: “This Node.js server will listen for incoming client requests on port 3000.”

You can access it via:
📍 http://localhost:3000

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🧪 Real-World Applications of Node.js Web Servers

Application Type	Description	Why Node.js?
REST APIs	Backend for mobile/web apps	Lightweight, fast, JSON-native
Real-time apps (chat)	Live messaging, notifications	Event-driven architecture (Socket.io)
File servers	Upload, download, manage files	Stream large files easily
Proxy servers	Intermediary for other services	Non-blocking and fast
Microservices	Independent backend services for large apps	Modular, scalable, and simple to deploy

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🔒 Security & Performance Tips

• Use https instead of http for secure communication.
• Implement rate-limiting and validation to prevent abuse.
• Use frameworks like Express.js for cleaner routing and middleware.
• Use clustering in Node.js to utilize multiple CPU cores.

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🧑‍💻 Lab Activity Ideas

1. ✅ Create a basic web server using Node.js that returns plain text.
2. 📄 Build a simple REST API that returns JSON data.
3. 🌐 Serve static HTML files from the server.
4. 🔁 Implement routing for /, /about, and /contact.
5. 📦 Use Express.js to replicate the same server with simplified code.

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📝 Summary

Concept	Key Takeaway
Node.js Web Server	Lightweight, event-driven server
Client Request	Comes via HTTP from browser or other tools
Server Response	Sends back data in HTML, JSON, or files
Port Listening	Server listens on a port like 3000
Routing	Use conditional logic or Express routes