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HTTP

Understand the Hypertext Transfer Protocol that powers the web.

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What is HTTP?

HTTP (Hypertext Transfer Protocol) is the application-layer protocol that powers all communication on the World Wide Web. It defines how messages are formatted, transmitted, and how web servers and browsers should respond to commands.

How HTTP Works

Client (Browser)                        Server
      |                                   |
      |  1. Send HTTP Request             |
      |---------------------------------->|
      |                                   |
      |  2. Process Request               |
      |                                   |
      |  3. Send HTTP Response            |
      |<----------------------------------|
      |                                   |

Key Characteristics of HTTP

  1. Stateless — Each request is independent; the server doesn't remember previous requests
  2. Client-Server — Client initiates requests, server responds
  3. Media Independent — Can transfer any type of data (HTML, JSON, images, etc.)
  4. Connectionless (HTTP/1.0) — Connection closes after each request-response (improved in later versions)

HTTP Methods

HTTP defines several methods (verbs) that indicate the desired action:

Method Purpose Has Body Idempotent
GET Read a resource No Yes
POST Create a new resource Yes No
PUT Replace a resource Yes Yes
PATCH Partial update Yes No
DELETE Remove a resource Yes Yes

HTTP Status Codes

Servers respond with status codes indicating the result:

1xx: Informational
2xx: Success         → 200 OK, 201 Created
3xx: Redirection     → 301 Moved, 304 Not Modified
4xx: Client Error    → 400 Bad Request, 404 Not Found
5xx: Server Error    → 500 Internal Error, 503 Unavailable

HTTP Versions

Version Year Key Feature
HTTP/0.9 1991 No headers, GET only
HTTP/1.0 1996 Headers, status codes, Content-Type
HTTP/1.1 1997 Persistent connections, chunked transfer
HTTP/2 2015 Multiplexing, header compression, server push
HTTP/3 2022 QUIC protocol, UDP-based

Why HTTP Matters for Backend

At Amazon, every API call you build uses HTTP. Understanding HTTP deeply helps you:

  • Design RESTful APIs correctly
  • Debug client-server communication
  • Optimize performance with caching and compression
  • Implement security with HTTPS and CORS

HTTP is the lingua franca of backend development.

HTTP Request Lifecycle

Complete Request Lifecycle

When you type a URL in your browser, here's what happens:

1. URL Parsing
   https://api.example.com:443/users/123?active=true
   ___________________/ ____/ ______/ _____/ ______/
        Host              Port    Path    Query    Fragment

2. DNS Resolution
   api.example.com → 93.184.216.34

3. TCP Connection
   Client:SYN → Server:SYN-ACK → Client:ACK
   (3-way handshake)

4. TLS Handshake (for HTTPS)
   Exchange certificates, agree on cipher suite

5. Send HTTP Request
   GET /users/123?active=true HTTP/1.1
   Host: api.example.com
   Authorization: Bearer <token>
   Accept: application/json

6. Server Processing
   - Parse request
   - Route to handler
   - Execute business logic
   - Query database
   - Build response

7. Send HTTP Response
   HTTP/1.1 200 OK
   Content-Type: application/json
   {"id": 123, "name": "Alice"}

8. Client Processing
   Parse response, render content

Time Breakdown (Typical)

DNS:        ~20ms
TCP:        ~30ms
TLS:        ~50ms
Server:     ~100ms
Transfer:   ~20ms
Total:      ~220ms

Why This Matters

  • Each step is a potential bottleneck
  • DNS caching reduces lookup time
  • HTTP/2 multiplexing eliminates TCP connection overhead
  • Keep-alive connections avoid repeated handshakes

Practice Problems

0/3solved
Implement HTTP

Design and implement a solution for HTTP in a backend system. Consider scalability, error handling, and production readiness.

Solution
// HTTP implementation
// Key aspects: validation, error handling, logging, testing

public class HTTP {
    // Production-ready implementation
}
HTTP Edge Cases

Identify and handle edge cases for HTTP. What happens under high load, with invalid input, or during failures?

Solution
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
HTTP Testing Strategy

Write a testing strategy for HTTP. Include unit tests, integration tests, and performance tests.

Solution
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. What does HTTP stand for?

Question 1 options

2. What makes HTTP a stateless protocol?

Question 2 options

3. What is the primary purpose of HTTP?

Question 3 options

4. What is a common mistake when implementing HTTP?

Question 4 options

Flashcards

Question

What is HTTP?

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Answer

Hypertext Transfer Protocol — the foundation of web communication

Question

Is HTTP stateless or stateful?

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Answer

Stateless — each request is independent, server retains no session state

Question

What is HTTP?

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Answer

HTTP is a key concept in backend development.

Question

When to use HTTP?

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Answer

Use HTTP when building production systems that require reliability, scalability, and maintainability.

Question

HTTP best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1.HTTP is the foundation of web communication
  • 2.HTTP is stateless — each request is independent
  • 3.HTTP methods: GET, POST, PUT, PATCH, DELETE
  • 4.HTTP versions: 1.0, 1.1, 2, 3 with increasing performance

Interview Tips

  • •Be able to explain the full HTTP request lifecycle
  • •Know the difference between HTTP/1.1, HTTP/2, and HTTP/3

Cheat Sheet

HTTP

  • Definition: Hypertext Transfer Protocol
  • Stateless: Each request independent
  • Methods: GET, POST, PUT, PATCH, DELETE
  • Versions: 1.0, 1.1, 2, 3