HTTP (Hypertext Transfer Protocol)

Description

HTTP (Hypertext Transfer Protocol) is an application-layer protocol used for transmitting hypermedia documents, such as HTML, over the web. It forms the foundation of data communication for the World Wide Web, enabling web browsers and servers to communicate using request-response protocols.

HTTP defines how messages are formatted and transmitted, and what actions web servers and browsers should take in response to various commands. Every time you visit a website, your browser sends HTTP requests to the web server and receives HTTP responses.

Key Characteristics

Stateless: Each request is independent; the server does not retain information about previous interactions.
Text-based: Human-readable format using plain text.
Flexible: Supports multiple content types (HTML, JSON, images, etc.).
Extensible: Allows for additional headers and methods.
Connectionless (by default): Each connection is established and closed per request, although HTTP/1.1 introduced keep-alive and HTTP/2 multiplexes requests.

HTTP Request Structure

An HTTP request typically includes:

Request Line (method, URL, HTTP version)
Headers (metadata)
Optional Body (for POST/PUT requests)

Example Request:

GET /index.html HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0
Accept: text/html

HTTP Response Structure

An HTTP response consists of:

Status Line (protocol version, status code, reason phrase)
Headers (metadata)
Body (content)

Example Response:

HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 1256

<html>...</html>

HTTP Methods

Method	Description
GET	Retrieve data from server
POST	Submit data to server
PUT	Update resource
DELETE	Delete specified resource
HEAD	Same as GET, but without response body
OPTIONS	Returns allowed methods for a resource
PATCH	Partially update resource

Status Codes

HTTP status codes are grouped into five classes:

Code Range	Meaning
1xx	Informational
2xx	Success
3xx	Redirection
4xx	Client Error
5xx	Server Error

Common Codes:

200 OK – Successful request
301 Moved Permanently – Redirect
400 Bad Request – Malformed request
403 Forbidden – No permission
404 Not Found – Resource not found
500 Internal Server Error – Server malfunction

Headers

Headers allow the client and server to send metadata:

Common Request Headers:

Host: Target domain
User-Agent: Client software info
Accept: Media types supported
Authorization: Authentication credentials

Common Response Headers:

Content-Type: Format of response
Content-Length: Size of response body
Set-Cookie: Server-sent cookie
Cache-Control: Caching behavior

HTTP Versions

Version	Features
HTTP/1.0	Basic request/response, no persistent connections
HTTP/1.1	Persistent connections, chunked transfer encoding
HTTP/2	Binary framing, multiplexing, header compression
HTTP/3	Based on QUIC (UDP), improved latency and security

Secure HTTP (HTTPS)

HTTPS is the secure version of HTTP using TLS/SSL encryption. It:

Protects data in transit
Authenticates the server
Prevents tampering and eavesdropping

HTTPS is standard for all modern websites.

HTTP vs HTTPS

Feature	HTTP	HTTPS
Port	80	443
Encryption	None	TLS/SSL
Secure	No	Yes
SEO Benefit	No	Yes

HTTP and REST APIs

HTTP is the foundation for RESTful APIs (Representational State Transfer), where resources are represented by URIs and standard HTTP methods are used for CRUD operations:

GET – Read
POST – Create
PUT – Update
DELETE – Delete

Example:

GET /api/users/123 HTTP/1.1
Host: api.example.com

Tools for HTTP Debugging

Browser Developer Tools (Network tab)
Postman – for API testing
curl – command-line HTTP client
Fiddler / Wireshark – traffic inspection

Summary

HTTP is the backbone of web communication. Understanding how it works—from methods and status codes to headers and versions—empowers developers to build efficient, secure, and scalable web applications. With the rise of REST APIs, microservices, and HTTP/2/3, mastering HTTP is more relevant than ever.