🌐 What is HTTP?

📖 Definition

HTTP (HyperText Transfer Protocol) is the protocol for exchanging data on the web. It defines the communication rules between clients (browsers) and servers, and is the fundamental technology underlying the web.

🎯 Understanding through Analogy

Postal System

Comparing HTTP to a postal system:

Sending a Letter (HTTP Request)
├─ Sender: Client (Browser)
├─ Recipient: Server
├─ Letter Content: Request Data
└─ Postal Rules: HTTP Protocol

Receiving a Reply (HTTP Response)
├─ Sender: Server
├─ Recipient: Client
├─ Reply Content: Response Data
└─ Status: Success/Failure

Restaurant Order

Customer (Client)
  ↓ Looking at Menu (GET Request)
Waiter (HTTP)
  ↓ Order Transmission
Kitchen (Server)
  ↓ Preparing Food
Waiter (HTTP)
  ↓ Food Delivery (Response)
Customer (Client)

💡 Core HTTP Concepts

Request and Response

Client ────Request───→ Server
            ←───Response────

Request

Client communicates what they want to the server
Composed of method, URL, headers, and body

Response

Server delivers the result of the client's request
Composed of status code, headers, and body

HTTP Characteristics

1. Statelessness
   ├─ Each request is independent
   ├─ Does not remember previous requests
   └─ State managed via cookies/sessions

2. Client-Server Architecture
   ├─ Role separation
   ├─ Client: UI/UX
   └─ Server: Data/Business Logic

3. Connectionless
   ├─ Connection closed after request-response
   ├─ Server resource conservation
   └─ Can be improved with Keep-Alive

📚 Series Documents

This series covers HTTP core concepts step by step:

1. HTTP Methods

GET, POST, PUT, DELETE, etc.

Types and purposes of HTTP methods
RESTful API design
Idempotency and safety
Practical examples

2. HTTP Status Codes

200, 404, 500, etc.

2xx (Success), 4xx (Client Error), 5xx (Server Error)
Meaning of each status code
Frequently seen codes in practice
Error handling methods

3. HTTP Headers

Request/Response Headers

Role and types of headers
Content-Type, Authorization, etc.
CORS related headers
Caching headers

4. Cookies and Sessions

State Management

Overcoming HTTP statelessness
Cookie operation principles
Session vs Token
Security considerations

🔍 HTTP Evolution

HTTP/0.9 (1991)
├─ Supported only GET method
└─ Transmitted HTML only

HTTP/1.0 (1996)
├─ Introduced header concept
├─ Added POST, HEAD
└─ Introduced status codes

HTTP/1.1 (1997)
├─ Keep-Alive by default
├─ Pipelining
├─ Added PUT, DELETE, etc.
└─ Host header mandatory

HTTP/2 (2015)
├─ Binary protocol
├─ Multiplexing
├─ Header compression
└─ Server push

HTTP/3 (2022)
├─ QUIC based (UDP)
├─ Faster connections
└─ Resistant to packet loss

💡 Practical Examples

Web Page Loading

1. Enter URL in browser
   https://example.com

2. DNS Lookup
   example.com → 93.184.216.34

3. Generate HTTP Request
   GET / HTTP/1.1
   Host: example.com
   User-Agent: Chrome/120.0

4. Server Response
   HTTP/1.1 200 OK
   Content-Type: text/html

   <html>...</html>

5. Browser Rendering
   Display web page on screen

API Call Example

# GET Request - Data Retrieval
curl https://api.example.com/users

# POST Request - Data Creation
curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name": "John Doe"}'

# PUT Request - Data Modification
curl -X PUT https://api.example.com/users/1 \
  -H "Content-Type: application/json" \
  -d '{"name": "Jane Smith"}'

# DELETE Request - Data Deletion
curl -X DELETE https://api.example.com/users/1

🤔 Frequently Asked Questions

Q1. Difference between HTTP and HTTPS?

HTTP (Port 80)
├─ Plain text communication
├─ Security vulnerable
└─ http://

HTTPS (Port 443)
├─ SSL/TLS encryption
├─ Data protection
├─ Requires certificate
└─ https://

Key differences:
- HTTPS encrypts data during transmission
- Prevents man-in-the-middle attacks
- Beneficial for search engine optimization (SEO)
- Modern web standard

Q2. Why is HTTP stateless?

Reasons for statelessness:
1. Scalability
   ├─ Servers do not store state
   ├─ Can be distributed across multiple servers
   └─ Easy load balancing

2. Simplicity
   ├─ Each request is independent
   ├─ Simple server implementation
   └─ Easy disaster recovery

3. Resource Conservation
   ├─ Minimize memory usage
   └─ Efficient concurrent processing

State management methods:
- Cookies
- Sessions
- Tokens (JWT)
- Local storage

Q3. Relationship between REST API and HTTP?

REST (Representational State Transfer)
├─ Architectural style based on HTTP
├─ Maps HTTP methods to CRUD
└─ Resource-centric design

HTTP Methods and CRUD:
GET    → Read   (Retrieve)
POST   → Create (Create)
PUT    → Update (Full Update)
PATCH  → Update (Partial Update)
DELETE → Delete (Delete)

RESTful API Example:
GET    /users      - List users
GET    /users/1    - Get specific user
POST   /users      - Create new user
PUT    /users/1    - Update user information
DELETE /users/1    - Delete user

🎓 Recommended Learning Path

Stage 1: Fundamental Concepts
├─ What is HTTP? (Current document)
├─ Request/Response Structure
└─ Client-Server Model

Stage 2: HTTP Methods
├─ GET, POST, PUT, DELETE
├─ Purpose of each method
└─ RESTful Design

Stage 3: Status Codes
├─ Meaning of 2xx, 4xx, 5xx
├─ Common codes
└─ Error Handling

Stage 4: Headers
├─ Request/Response Headers
├─ Content-Type
└─ Authentication Headers

Stage 5: State Management
├─ Cookies and Sessions
├─ Token-based Authentication
└─ Security Considerations

How Do Browsers Work? - How HTTP is used in browsers
What is an API? - Concept of HTTP-based APIs
What is HTTPS? - Secure version of HTTP
What is CORS? - Cross-Origin Policy for HTTP

🎬 Conclusion

HTTP is the most fundamental protocol in web development. Learn its core concepts step by step through this series!

Next Step: Read HTTP Methods to learn more about GET, POST, and other methods in detail.

📖 Definition​

🎯 Understanding through Analogy​

Postal System​

Restaurant Order​

💡 Core HTTP Concepts​

Request and Response​

HTTP Characteristics​

📚 Series Documents​

1. HTTP Methods​

2. HTTP Status Codes​

3. HTTP Headers​

4. Cookies and Sessions​

🔍 HTTP Evolution​

💡 Practical Examples​

Web Page Loading​

API Call Example​

🤔 Frequently Asked Questions​

Q1. Difference between HTTP and HTTPS?​

Q2. Why is HTTP stateless?​

Q3. Relationship between REST API and HTTP?​

🎓 Recommended Learning Path​

🔗 Related Documents​

🎬 Conclusion​