HTTP and Web

What is HTTP?

HTTP = Hyper Text Transfer Protocol
Used to transfer web pages.

• Stateless (no memory between requests)
• Uses port 80
• Text-based communication

HTTPS = Secure HTTP (encrypted)
Uses port 443

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Client-Server Architecture

Client: Requests data
Server: Responds with data

Examples:

• Browser → Client
• Website → Server

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HTTP Methods

Method	Use
GET	Read data
POST	Send/Create data
PUT	Update data
DELETE	Delete data
PATCH	Partial update
HEAD	Header only
OPTIONS	Check available methods

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HTTP Status Codes

Success (2xx)

Code	Meaning
200	OK — Successful
201	Created
204	No Content

Redirect (3xx)

Code	Meaning
301	Moved Permanently
302	Found
304	Not Modified

Client Errors (4xx)

Code	Meaning
400	Bad Request
401	Unauthorized
403	Forbidden
404	Not Found

Server Errors (5xx)

Code	Meaning
500	Internal Server Error
502	Bad Gateway
503	Service Unavailable

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URL Breakdown

Example:

https://www.example.com:443/home/index.html?user=1

Component	Value
Protocol	https
Subdomain	www
Domain	example.com
Port	443
Path	/home/index.html
Query	?user=1

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APIs

API = Application Programming Interface
Allows communication between applications.

Examples:

• Mobile app talking to server
• Weather app fetching weather data

Types of APIs

Type	Description
REST	Resource-based, uses HTTP methods
GraphQL	Query language for APIs
SOAP	XML-based, more structured

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Cookies vs Sessions vs Local Storage

Feature	Cookies	Sessions	Local Storage
Stored Where?	Browser	Server	Browser
Data Lifetime	Set by expiry	Until user logs out / expires	Until manually cleared
Size Limit	~4KB	Depends on server	~5–10MB
Security	Can be stolen if not secured	More secure	Less secure
Accessible By	Client + Server	Server only	Client (JavaScript)
Best For	Auth tokens, tracking, remember me	Login session, user identity	Preferences, theme, small app data
Automatically Sent to Server?	Yes (with every request)	No	No
Works Offline?	Yes	No	Yes

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What Happens When You Type google.com in Browser?

1. DNS Resolution — Domain resolves to IP
2. TCP Connection — Browser connects to server
3. TLS Handshake — HTTPS encryption established
4. HTTP Request — Browser sends GET request
5. Server Response — Server returns HTML
6. Page Rendering — Browser displays content

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WebSocket

Allows real-time two-way communication.

Unlike HTTP which is request-response only, WebSocket keeps a persistent connection.

Used in:

• Chat applications
• Online games
• Live tracking
• Stock trading platforms
• Real-time notifications

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Quick Reference

Protocol	Port	Encrypted
HTTP	80	No
HTTPS	443	Yes