Most web systems communicate using HTTP or WebSockets. Understanding when to use each is crucial for system design.

1. HTTP (HyperText Transfer Protocol)

HTTP is a request-response protocol. The client sends a request, and the server sends a response.

• Stateless: Each request is independent.
• Methods: GET, POST, PUT, DELETE, PATCH.
• Status Codes: 2xx (Success), 3xx (Redirection), 4xx (Client Error), 5xx (Server Error).

HTTP Versions

• HTTP/1.1: Persistent connections, but suffers from "Head-of-Line Blocking" (one slow request blocks others).
• HTTP/2: Multiplexing (many requests over one connection), Server Push, Header Compression.
• HTTP/3: Uses QUIC (UDP-based) to reduce latency and handle packet loss better.

2. HTTPS (HTTP Secure)

HTTPS is HTTP over TLS/SSL. It provides:

• Encryption: Protects data from eavesdropping.
• Integrity: Prevents tampering.
• Authentication: Verifies the identity of the server.

3. WebSockets

Unlike HTTP, WebSockets provide a full-duplex, persistent connection between client and server.

• Real-time: Server can push data to the client without the client asking.
• Low Overhead: Once the connection is established (via an HTTP handshake), there are no HTTP headers sent with every message.
• Use Cases: Chat applications, live sports scores, collaborative editing, stock tickers.