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What is SignalR and how does it work in real-time web applications?

Utpal Vishwas 93 21-May-2025
c# c#  signalr 
Updated on 21-May-2025
Utpal Vishwas

Utpal Vishwas

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I am Utpal Vishwas from Uttar Pradesh. Have completed my B. Tech. course from MNNIT campus Prayagraj in 2022. I have good knowledge of computer networking.

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Utpal Vishwas

Utpal Vishwas

21-May-2025

What is SignalR?

SignalR is a Microsoft library (part of ASP.NET) that simplifies adding real-time web functionality to applications. Real-time means that the server can push content updates instantly to connected clients without the clients having to ask (poll) repeatedly.

Why is SignalR needed?

In traditional web apps, the client (browser) must frequently send requests to the server to check for updates (polling), which is inefficient and introduces latency.

SignalR enables:

  • Instant communication: Server can push updates immediately.
  • Bidirectional communication: Client and server can send messages back and forth anytime.
  • Automatic transport selection: SignalR abstracts the underlying communication method and picks the best available protocol.

How does SignalR work?

  1. Connection Establishment: When a client connects, SignalR negotiates the best transport protocol supported by both client and server:
    1. WebSockets (best performance, full-duplex)
    2. Server-Sent Events (SSE)
    3. Long Polling (fallback if others aren’t supported)
  2. Hubs: SignalR uses the concept of hubs — high-level pipelines that allow clients and servers to call methods on each other directly.
  3. Messaging: 
    1. The server can call methods on connected clients to push data (e.g., new chat messages, live scores, notifications).
    2. Clients can invoke server-side methods to send data or requests.
  4. Groups: Clients can be grouped logically, so messages can be sent to specific subsets (like a chat room or user group).

Example Use Cases

  1. Chat applications: Users see messages instantly.
  2. Live dashboards: Real-time updates on metrics.
  3. Online games: Synchronize game states across players.
  4. Collaboration tools: Instant notifications and updates.
  5. Auction sites: Show bids as they happen.

Summary

Feature Description
Real-time Server pushes updates instantly
Transport Automatically picks best protocol
Bidirectional Client and server can call each other
Groups Target messages to specific clients

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