Get Started with SignalR: a Chat Room Example

In this sample you'll learn how to use ASP.NET Core SignalR to build a chat room application.

This tutorial is to give you a brief introduction about how ASP.NET Core SignalR works, if you're already familiar with it, you can skip this sample.

Please be noted this sample, and all other samples in this repo, are based on ASP.NET Core SignalR rather than the ASP.NET version.

Our chat room is a web page application that anyone can login to and chat with other users in the room.

The first time you open the application you'll be asked for your name:

Then you can send a message and everyone in the room can see it:

Let's implement this feature step by step.

First create a ASP.NET Core web application.
```
dotnet new web
```
Before you start, make sure you installed the latest .NET Core 2.1 SDK.
Create a Chat.cs that defines a Chat hub class.
```
using Microsoft.AspNetCore.SignalR;

public class Chat : Hub
{
    public void BroadcastMessage(string name, string message)
    {
        Clients.All.SendAsync("broadcastMessage", name, message);
    }

    public void Echo(string name, string message)
    {
        Clients.Client(Context.ConnectionId).SendAsync("echo", name, message + " (echo from server)");
    }
}
```
SignalR SDK is already included in Microsoft.AspNetCore.App package reference in ChatRoomLocal.csproj file.

Hub is the core concept in SignalR which exposes a set of methods that can be called from clients. Here we define two methods: Broadcast() which broadcasts the message to all clients and Echo() which sends the message back to the caller.

In each method you can see there is a Clients interface that gives you access to all connected clients so you can directly call back to these clients.
Then we need to initialize the SignalR runtime when the application starts up. Add the following in Startup.cs:
```
public void ConfigureServices(IServiceCollection services)
{
    services.AddSignalR();
}

public void Configure(IApplicationBuilder app)
{
    ...
    app.UseSignalR(routes =>
    {
        routes.MapHub<Chat>("/chat");
    });
}
```
Make sure you remove app.Run(...) from Configure(), which will always give you a Hello World page.

The key changes here are AddSignalR() which initializes the SignalR runtime and MapHub() which maps the hub to the /chat endpoint so clients can access the hub using this url.

The last step is to create the UI of the chat room. In this sample, we will use HTML and Javascript to build a web application:

Copy the HTML and script files from wwwroot of the sample project to the wwwroot folder of your project. Add the following code to Startup.cs to make the application serve the pages:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    ...
    app.UseFileServer();
}

Let's take a look at key changes in index.html. First it creates a hub connection to the server:

var connection = new signalR.HubConnectionBuilder()
                            .withUrl('/chat')
                            .build();

When the user clicks the send button, it calls broadcastMessage() to broadcast the message to other clients:

document.getElementById('sendmessage').addEventListener('click', function (event) {
    // Call the broadcastMessage method on the hub.
    if (messageInput.value) {
        connection.send('broadcastMessage', username, messageInput.value);
    }
    ...
});

Also, it registers a callback to receive messages from the server:

var messageCallback = function(name, message) {
    if (!message) return;
    // Html encode display name and message.
    var encodedName = name;
    var encodedMsg = message.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
    var messageEntry = createMessageEntry(encodedName, encodedMsg);

    var messageBox = document.getElementById('messages');
    messageBox.appendChild(messageEntry);
    messageBox.scrollTop = messageBox.scrollHeight;
};
// Create a function that the hub can call to broadcast messages.
connection.on('broadcastMessage', messageCallback);

Now, build and run the application:

dotnet build
dotnet run

You can also use dotnet watch run to watch and reload the code changes.

Open http://localhost:5000, and you'll see the chat room running on your local machine.

In this sample you have learned the basics of SignalR and how to use it to build a chat room application. In other samples you'll learn how to use Azure SignalR service and host your chat room on Azure.

danielscholl/signalr-sample

Get Started with SignalR: a Chat Room Example