What is HTTP?

HTTP (Hypertext Transfer Protocol) is the foundation of data communication on the web. It's a request-response protocol where clients send requests and servers return responses.

HTTP Request Structure

GET /api/users/123 HTTP/1.1
Host: api.example.com
Authorization: Bearer token123
Content-Type: application/json
Accept: application/json

Component	Description
Method	GET, POST, PUT, DELETE, PATCH
Path	Resource URL
Headers	Metadata (auth, content type)
Body	Data payload (POST, PUT, PATCH)

HTTP Methods

Method	Purpose	Idempotent	Safe
GET	Retrieve resource	Yes	Yes
POST	Create resource	No	No
PUT	Replace resource	Yes	No
PATCH	Partial update	No	No
DELETE	Remove resource	Yes	No

HTTP Status Codes

Range	Category	Examples
2xx	Success	200 OK, 201 Created, 204 No Content
3xx	Redirection	301 Moved, 304 Not Modified
4xx	Client Error	400 Bad Request, 401 Unauthorized, 404 Not Found
5xx	Server Error	500 Internal Error, 502 Bad Gateway, 503 Unavailable

HTTP/1.1 vs HTTP/2 vs HTTP/3

Feature	HTTP/1.1	HTTP/2	HTTP/3
Multiplexing	No	Yes	Yes
Header compression	No	HPACK	QPACK
Server push	No	Yes	Yes
Transport	TCP	TCP	QUIC (UDP)
Head-of-line blocking	Yes	Partially	No

Connection Management

HTTP/1.1

Connection: keep-alive  # Reuse TCP connection
Connection: close       # Close after response

Connection Pooling

┌─────────┐     ┌─────────────┐     ┌─────────┐
│ Client  │────►│ Conn Pool   │────►│ Server  │
└─────────┘     │ [conn1]     │     └─────────┘
                │ [conn2]     │
                │ [conn3]     │
                └─────────────┘

Interview Tips

Know HTTP methods and their semantics
Understand status code categories
Explain HTTP/2 improvements (multiplexing)
Discuss connection management and keep-alive
Mention idempotency for retry safety

HTTP

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