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HTTP Status Codes

Master all HTTP status code categories and when to use each.

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Status Code Categories

HTTP status codes indicate the result of a server's attempt to process a request. They are grouped into five categories:

Status Code Categories

┌──────┬──────────────┬───────────────────────────────────┐
│ Code │ Category     │ Meaning                           │
├──────┼──────────────┼───────────────────────────────────┤
│ 1xx  │ Informational│ Request received, processing      │
│ 2xx  │ Success      │ Request successfully received     │
│ 3xx  │ Redirection  │ Further action needed             │
│ 4xx  │ Client Error │ Invalid request from client       │
│ 5xx  │ Server Error │ Server failed to fulfill request  │
└──────┴──────────────┴───────────────────────────────────┘

1xx Informational

Code Name Use
100 Continue Client can send body
101 Switching Protocols Protocol upgrade (WebSocket)

2xx Success

Code Name Use
200 OK Successful GET, PUT, PATCH
201 Created Successful POST (resource created)
202 Accepted Request accepted for async processing
204 No Content Successful DELETE (no response body)

3xx Redirection

Code Name Use
301 Moved Permanently URL has changed permanently
302 Found Temporary redirect
304 Not Modified Cached response is still valid

4xx Client Error

Code Name Use
400 Bad Request Malformed request syntax
401 Unauthorized Authentication required
403 Forbidden Authenticated but not authorized
404 Not Found Resource doesn't exist
405 Method Not Allowed HTTP method not supported
409 Conflict Resource state conflict
422 Unprocessable Entity Validation failed
429 Too Many Requests Rate limit exceeded

5xx Server Error

Code Name Use
500 Internal Server Error Unexpected server failure
502 Bad Gateway Upstream server returned invalid response
503 Service Unavailable Server temporarily overloaded
504 Gateway Timeout Upstream server timeout

HTTP Best Practices

Methods

  • GET: Read (safe, idempotent)
  • POST: Create
  • PUT: Replace (idempotent)
  • PATCH: Partial update
  • DELETE: Remove (idempotent)

Headers

  • Content-Type: Body format
  • Cache-Control: Caching rules
  • Authorization: Authentication
  • Accept: Desired response format

Status Codes

  • 2xx: Success
  • 3xx: Redirection
  • 4xx: Client error
  • 5xx: Server error

Key Points

  • Understanding HTTP Status Codes is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0/3solved
Implement HTTP Status Codes

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

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

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

Identify and handle edge cases for HTTP Status Codes. 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 Status Codes Testing Strategy

Write a testing strategy for HTTP Status Codes. 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 status code should you return when rate limiting a client?

Question 1 options

2. What is the difference between 401 and 403?

Question 2 options

3. What is the primary purpose of HTTP Status Codes?

Question 3 options

4. What is a common mistake when implementing HTTP Status Codes?

Question 4 options

Flashcards

Question

What does 404 mean?

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Answer

Not Found — the requested resource doesn't exist

Question

Difference between 401 and 403?

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Answer

401 = not authenticated (needs login). 403 = not authorized (insufficient permissions)

Question

What is HTTP Status Codes?

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Answer

HTTP Status Codes is a key concept in backend development.

Question

When to use HTTP Status Codes?

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Answer

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

Question

HTTP Status Codes 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

  • 1.1xx=info, 2xx=success, 3xx=redirect, 4xx=client error, 5xx=server error
  • 2.201 for creation, 204 for deletion with no body
  • 3.401=unauthenticated, 403=unauthorized
  • 4.429 for rate limiting

Interview Tips

  • •Know the meaning of all common status codes
  • •Understand when to use 401 vs 403

Cheat Sheet

Status Codes

  • 200: OK, 201: Created, 204: No Content
  • 301: Permanent Redirect, 304: Not Modified
  • 400: Bad Request, 401: Unauthorized, 403: Forbidden
  • 404: Not Found, 422: Validation Error, 429: Rate Limited
  • 500: Server Error, 502: Bad Gateway, 503: Unavailable