Why use signalr

SignalR is an open source library to add real-time web functionality in your ASP. Net web application. 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.

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. 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. NET Core version is the one we will focus on in this article; although most of the benefits apply equally well to the ASP.

NET classic version. If you want to create your own implementation of a WebSocket server, good luck. Of course, it is doable, but there are way too many things to take care of. For example, you will probably have to split your messages into streams of bytes of the equal size and send them in sequence. So, your code will probably look something like this:.

So, already there are some decision to make. What is the size of each byte array? And how do you clean up unused elements from the last byte array to reconstruct the message into its original form?

This is why both your client and your server will have to have something like this:. And what do you do if one of the message chunk fails to get transmitted?

In this case, you will have to write quite a lot of extra code to handle other transport mechanisms. With SignalR, none of these will matter. The code is so simple that it looks almost like you can directly call methods on the server from a client and vice versa. Yes, SignalR works with any types of client and not necessarily web pages. We will cover more of this later. Of course, remote method calling is not what actually happens under the hood.

But all complex implementation details have been abstracted away, so this is not something you, as a developer, will have to worry about. Likewise, the code will be exactly the same regardless of which transport mechanisms you use. But the code will still look the same regardless. Back in the days, AJAX was a standard way of making partial updates to a web page by asynchronously retrieving some data chunks from the server.

This was especially popular when jQuery was used everywhere. AJAX was completely fine when all you needed was to retrieve data from the server when some user-initiated action happened on the web page. But what if you needed to retrieve new data as soon as it becomes available?

With AJAX, you would have to implement some sort of logic that queries the server at regular intervals. This would make real-time applications, such as chat, fairly inefficient and not necessarily fully synchronized in time. Your client will automatically receive the update as soon as the data is available. To use the SignalR client library, import the Microsoft. Client package from NuGet. The following console application uses the HubConnectionBuilder from the SignalR client library to configure the hub connection.

The syntax is similar to the JavaScript client. You can add methods that are invoked by the hub. Listing 4 is a console application that uses the library to connect to the SignalR hub you built earlier. When run, the application prompts for a username and password, and then uses the credentials to request a token from the token endpoint you created previously.

It then connects to the SignalR hub and displays any messages that are sent. Send messages by typing into the console, as shown in Figure 4. NET SignalR automatically handles restarting the connection when a disconnection occurs. Reconnection behavior is often specific to each application.

For this reason, ASP. For most common scenarios, a client only needs to reconnect to the hub when a connection is lost or a connection attempt fails. To do this, the application can listen for these events and call the start method on the hub connection. Here's how it looks in JavaScript, adding reconnection logic when a connection is closed or a connection attempt has failed.

A common requirement for real-time applications is to track which users are currently online. A basic way to add presence to an ASP. Because a single user identity can potentially have more than one connection to the hub, the application needs to track the number of connections per user. Listing 5 shows a simple class that implements a user tracker.

Whenever a connection is opened or closed, ConnectionOpened or ConnectionClosed is called. Based on the number of connections for the user associated with the connection event, the methods return a status to indicate if user has joined or left. In the hub, call the tracker in Listing 6 and broadcast a message when a user has joined or left.

Also, send the list of currently online users when a connection is created, as shown in Listing 6. Now when users join or leave the chat application, a system message appears, as shown in Figure 5. This example gets you started in creating a presence system for your SignalR hub, but a more robust solution will be required to handle scale-out and server restarts. In order for ASP. NET Core applications running SignalR to scale out to more than one instance, a backplane must be set up.

Instances communicate over the backplane to ensure that messages reach the correct destinations no matter which clients are connected to which instances. However, a much simpler way to scale out your ASP. SignalR Service handles the scale-out for you, so you can support large numbers of connections without setting up a backplane yourself. SignalR NuGet package. Now when you run the application, instead of directly connecting to the hub in your ASP.

This allows you to scale the service up and down at any time to handle different levels of traffic without any modifications to the application's code or hosting environment. Note that the ASP. SignalR Service supports JWT authorization as well, but its integration is beyond the scope of this article.

As you can see, adding real-time Web functionalities to your cross-platform Web applications is easy using ASP. And with the Azure SignalR Service, you now have a fully managed backplane for highly scalable applications. My Subscriber Account Advertise Write. Training Home State of. Staffing Home Looking for Staff? Looking for Work? Contact Us. Dark Kimbie. Published in:. Filed under: SignalR. NET Core articles All major programming platforms have frameworks that make it easier to build real-time applications.

Introducing ASP. JavaScript Client Library In the browser, the biggest change is the removal of the jQuery dependency. Dependency Injection ASP. Reconnections Another design decision that seemed like a good idea when SignalR first came out was automatic reconnections. Get Started with ASP. SignalR --version 1. Hub: using System. Tasks; using Microsoft.

SignalR; namespace SignalRChat. UseAuthentication ; app. UseMvc ; app. Figure 1: Run the SignalR chat application. Add Authentication and Authorization SignalR authentication and authorization use the same claims-based identity infrastructure provided by ASP. SendAsync "newMessage", Context. Figure 2: The authenticated username appears in the chat. GetBytes Configuration["JwtKey"] ; services.

AddPolicy JwtBearerDefaults. AuthenticationScheme ; policy. RequireClaim ClaimTypes. Tokens; using System. Jwt; using System. Claims; using System. Authorization; using Microsoft. Identity; using Microsoft. Mvc; using Microsoft.

Configuration; using Microsoft. Tokens; using SignalRChat. Data; namespace SignalRChatDemo.