What, Why and How About SignalR

What is SignalR

We know very well how a client sends data to a server so now it's time to understand how a server pushes data to a client in a HTTP connection. SignalR is an open source library to add real-time web functionality in your ASP.Net web application. So what does real-time functionality mean? Just use as an example when more than 1 user is working on the same document in Google Documents When a user is making changes and at the same time another user can see the changes without reloading the page. So real-time web functionality is the ability to have server code to push content to connected clients. In the HTTP request response model we know each time we need to send a new request to communicate with the server but SignalR provides a persistent connection between the client and server.

It can be easily scaled out via SQL Server, Redis or a service bus (scale out means adding more servers to handle the load). There is no need to worry about this scale out term, in my next article I will explain it in detail because SignalR provides good scale out features. SignalR uses Web socket technology to send data. WebSocket is a new HTML5 API that enables bidirectional communication between the browser and server but if it is not available then SignalR can use other technologies like long polling.

SignalR transfers data in non-compressed JSON text or plain text so if you want to send data in compressed JSON then you need to write your own logic on the server side and the same logic on the client side also. SingnalR makes extensive use of asynchronous techniques to achieve immediate and maximum performance.

Modes of communication

SignalR provides two models for communicate between clients and severs.

1. Persistent Connections

Persistent Connections provide direct access to a low-level communication protocol that signalR provides. Each client connection to a server is identified by a connectionID. So in your application if you need more control over a connection, in SingnalR you can use this model. This midel can be used where you want to work with a messaging and dispatching model rather than remote invocation or in any existing application using a message model and you want to port to signalR.

2. Hubs

Hubs provide a High level API for the client and server to call each other's method. It will be very familiar to those developers who have worked on remote invocation APIs. If you have multiple types of messages that you want to send between a server and a client then it is recommended to use Hubs so you don't need to do your own dispatching. You can create an application either using Hubs or a Persistent connection; the only concern is, with Hubs it will be easy to implement.





So now we have an idea of what SignalR is so now it's time to proceed to "why".

WHY use SignalR

Using SignalR we can create web applications that require high frequency updates from the server. For examle, a dashboard, games and chat applications. SignalR uses Web Sockets and the HTML5 API that helps in bidirectional communication. It also provides an API for server-to-client Remote Procedure Calls (RPC) call, it may be something new for you because most of the time we use a request and response model.

SignalR includes automatic connection management, it provides the facility to broadcast messages to all connected clients or to a specific client. The connection between the client and server is persistent while in HTTP it isn't persistent.

So now where to use SignalR: