SignalR Chat Application using Asp.Net Core

Today's modern apps are expected to deliver up-to-date information without hitting a refresh button. Add real-time functionality to your dashboards, maps, games and more.

What is real-time functionality? It's the ability to have your server-side code push content to connected clients as it happens, in real-time.
While chat is often used as an example, you can do a whole lot more. Any time a user refreshes a web page to see new data, or the page implements Ajax long polling to retrieve new data, it's a candidate for using SignalR.
SignalR also enables completely new types of applications that require high-frequency updates from the server, e.g. real-time gaming.

What is a SignalR hub

The SignalR Hubs API enables you to call methods on connected clients from the server. In the server code, you define methods that are called by the client. In the client code, you define methods that are called from the server. SignalR takes care of everything behind the scenes that makes real-time client-to-server and server-to-client communications possible.

Prerequisites

• Visual Studio 2017 version 15.9 or later with the ASP.NET and web development workload. You can use Visual Studio 2019, but some project creation steps differ from what's shown in the tutorial.
• .NET Core SDK 2.2 or later

Create a web project

• From the menu, select File > New Project.
• In the New Project dialog, select Installed > Visual C# > Web > ASP.NET Core Web Application. Name the project SignalRChat.

• Select Web Application to create a project that uses Razor Pages.
• Select a target framework of .NET Core, select ASP.NET Core 2.2, and click OK.

Add the SignalR client library
The SignalR server library is included in the Microsoft.AspNetCore.App metapackage. The JavaScript client library isn't automatically included in the project. For this tutorial, you use Library Manager (LibMan) to get the client library from unpkg. unpkg is a content delivery network (CDN)) that can deliver anything found in npm, the Node.js package manager.

• In Solution Explorer, right-click the project, and select Add > Client-Side Library.
• In the Add Client-Side Library dialog, for Provider select unpkg.
• For the Library, enter @aspnet/signalr@1, and select the latest version that isn't reviewed.

                                         Libman creates a wwwroot/lib/signalr folder and copies the selected files to it.

Create a SignalR hub A hub is a class that serves as a high-level pipeline that handles client-server communication.

• In the SignalRChat project folder, create a Hubs folder.
• In the Hubs folder, create a ChatHub.cs file with the following code:

          using Microsoft.AspNetCore.SignalR;

          using System.Threading.Tasks;

           namespace SignalRChat.Hubs

              {

                   public class ChatHub : Hub

                      {

                          public async Task SendMessage(string user, string message)

                             {

                                 await Clients.All.SendAsync("ReceiveMessage", user, message);

                              }

                         }

                 }

Configure SignalR

The SignalR server must be configured to pass SignalR requests to SignalR.

• Add the following highlighted code to the Startup.cs file.

    using Microsoft.AspNetCore.Builder;

using Microsoft.AspNetCore.Hosting;

using Microsoft.AspNetCore.Http;

using Microsoft.AspNetCore.Mvc;

using Microsoft.Extensions.Configuration;

using Microsoft.Extensions.DependencyInjection;

using SignalRChat.Hubs;

namespace SignalRChat

{

public class Startup

{

public Startup(IConfiguration configuration)

{

Configuration = configuration;

}

public IConfiguration Configuration { get; }

// This method gets called by the runtime. Use this method to add services to the container.

public void ConfigureServices(IServiceCollection services)

{

services.Configure<CookiePolicyOptions>(options =>

{

// This lambda determines whether user consent for non-essential cookies is needed for a given request.

options.CheckConsentNeeded = context => true;

options.MinimumSameSitePolicy = SameSiteMode.None;

});

services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

services.AddSignalR();

}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.

public void Configure(IApplicationBuilder app, IHostingEnvironment env)

{

if (env.IsDevelopment())

{

app.UseDeveloperExceptionPage();

}

else

{

app.UseExceptionHandler("/Error");

app.UseHsts();

}

app.UseHttpsRedirection();

app.UseStaticFiles();

app.UseCookiePolicy();

app.UseSignalR(routes =>

{

routes.MapHub<ChatHub>("/chatHub");

});

app.UseMvc();

}

}

}

These changes add SignalR to the ASP.NET Core dependency injection system and the middleware pipeline.

Add SignalR client code

• Replace the content in Pages\Index.cshtml with the following code:

         @page
<div class="container">
<div class="row">&nbsp;</div>
<div class="row">
<div class="col-6">&nbsp;</div>
<div class="col-6">
User..........<input type="text" id="userInput" />
<br />
Message...<input type="text" id="messageInput" />
<input type="button" id="sendButton" value="Send Message" />
</div>
</div>
<div class="row">
<div class="col-12">
<hr />
</div>
</div>
<div class="row">
<div class="col-6">&nbsp;</div>
<div class="col-6">
<ul id="messagesList"></ul>
</div>
</div>
</div>
<script src="~/lib/signalr/dist/browser/signalr.js"></script>
<script src="~/js/chat.js"></script>

The preceding code:
Creates text boxes for name and message text, and a submit button.
Creates a list with id="messagesList" for displaying messages that are received from the SignalR hub.
Includes script references to SignalR and the chat.js application code that you create in the next step.

• In the wwwroot/js folder, create a chat.js file with the following code:

"use strict";

var connection = new signalR.HubConnectionBuilder().withUrl("/chatHub").build();

//Disable send button until connection is established

document.getElementById("sendButton").disabled = true;

connection.on("ReceiveMessage", function (user, message) {

var msg = message.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");

var encodedMsg = user + " says " + msg;

var li = document.createElement("li");

li.textContent = encodedMsg;

document.getElementById("messagesList").appendChild(li);

});

connection.start().then(function(){

document.getElementById("sendButton").disabled = false;

}).catch(function (err) {

return console.error(err.toString());

});

document.getElementById("sendButton").addEventListener("click", function (event) {

var user = document.getElementById("userInput").value;

var message = document.getElementById("messageInput").value;

connection.invoke("SendMessage", user, message).catch(function (err) {

return console.error(err.toString());

});

event.preventDefault();

});

The preceding code:

Creates and starts a connection.

Adds to the submit button a handler that sends messages to the hub.

Adds to the connection object a handler that receives messages from the hub and adds them to the list.

Run the app

• Press CTRL+F5 to run the app without debugging.
• Copy the URL from the address bar, open another browser instance or tab, and paste the URL in the address bar.
• Choose either browser, enter a name and message, and select the Send Message button.
• The name and message are displayed on both pages instantly.