What is REST

REST (Representational state Transfer) is an architectural style for designing networked applications. Uses standard HTTP Methods.

Why Rest Matters?

It provides a simple and standard way for applications to communicate with each other over the internet.

• Scalability : REST APIs are usually stateless, which means each request contains all the information required by the server to process it. The server does not rely on information from previous requests.
• Interoperability: Works across different platform.
• Efficiency: Uses Caching, Statelessness for performance.
• Easy Integration: REST makes it easier to connect different systems.

Real time communication protocols

Real-time communication helps overcome these limitations by enabling faster and continuous data exchange.

• Polling
  • WebSocket’s 
  • Server-sent Events(SSE)
  • Long Polling

WebSocket’s: Persistent Full-Duplex Communication

• Definition: WebSocket’s provides a persistent, Full duplex Connection between the client and server over a single TCP connection.
• How they work:
  • WebSocket handshake using HTTP upgrade request.
    • Step-1: client request an upgrade to WebSocket’s.
• • • Step-2: Server accepts and keeps the connection open.
    Connection remains open for continuous data exchange.
  • Either client or server can send messages at any time.
    • Step-3: Data is exchanged in real-time using frame.
    • Step-4: Either party can close the connection when done.

Advantage of use cases of WebSocket’s

• Advantages:
  • Persistent connection = lower latency
  • Reduces overhead compared to HTTP polling.
  • Efficient for real-time applications.
• Use Cases:
  • Live chat Applications.
  • Stock Market price updates.
  • Multiplayer online Games.
  • Collaborative Tools.(Google Docs, Figma)

3. Long Polling: Simulating Real-Time With HTTP.

• Long polling is a technique in which the client sends a request to the server and waits until new data is available. Once the server has new information, it sends a response back to the client.
• How it differs from regular polling.
• Instead of sending an immediate response, the server keeps the request open until new data becomes available.
• How Long Polling Works
  • Client makes an HTTP requests.
  • Server holds the request until data is available.
  • Server responds with new data.
  • Client immediately sends another request.

2. Session Management

What is web Session

A wed session is a mechanism used to maintain the state of a users interaction Across multiple Http requests. Since Http is a state less protocol every request sent from a browser to a server is independent. the server does not inherently know wheteher two requests came from the same user, a session solve the problem.

Session lifecycle

1. User Authentication: user Submit request.

{
 "userName" : "rakesh",
 "password" : "pass,123@123"
}

Server Validates Credentials.

2. Session Creation : Server creates

{
 "sessionId":"ABC123",
 "userId" : "1001",
 "role" : "Admin"
}

Sore in session repository.

3. SessionId sent to browser

Response header:

setCookiejSESSIONID=xyz123

Browser store the cookie.

Why web session matter

• web applications often need to track user state (login status, shopping cart, user prefrences).
• Http is state less memory each request independent.
• goal to understand how to maintain state in web applications.

Understanding Statelessness in Http

• Http does not retain memory of previous requests.
• Each request must contain all necessary information.
• This is a challenges for user sessions.

Techniques for maintaining State

• Session-Based Authentication(server-side session storage + cookies for session Ids).
  • Server maintains session state.
  • Client holds only a sessionId.
• Token Based Authentication(JWT, OAuth, token)
  • Session state is Embedded within the token itself.
  • Server does not need to track user session.

1. Session Based Authentication

• Server-side session storage
• Cookies for session IDS.
• Once user logs in server creates a session & assigns a sessionID.
• Session data is stored server-side , while sessionID to sent to the client.
• Client store the sessionId in the cookie.

2. Token-based Authentication

• Encodes session data in a self contained token.
• No need for server-side session storage.
• Used in modern state less Authentication.