Blazor/Documentation/docusaurus/docs/bonus/websocket.md

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1	Websocket

This course explains how to get started with WebSockets in ASP.NET Core. WebSocket (RFC 6455) is a protocol that allows persistent two-way communication channels over TCP connections. Its use benefits applications that take advantage of fast, real-time communication, such as chat, dashboard, and game applications.

For our examples we will use a small example project available here.

WebSocket definition

In the traditional web paradigm, the client was responsible for initiating communication with a server, and the server could not send data back unless it had been previously requested by the client. With WebSockets, you can send data between server and client over a single TCP connection, and typically WebSockets are used to provide real-time functionality to modern applications.

What is a SignalR Hub?

The SignalR hubs API lets you call methods on connected clients from the server.

• In server code, you define methods that are called by the client.
• In client code, you define methods that are called from the server.

SignalR takes care of everything in the background that makes real-time client-to-server and server-to-client communications possible.

Install the SignalR .NET client package

The Microsoft.AspNetCore.SignalR.Client package is required for .NET clients to connect to SignalR hubs.

Install the Microsoft.AspNetCore.SignalR.Client package in its latest version.

Or using the Package Manager console: PM> Install-Package Microsoft.AspNetCore.SignalR.Client

Use SignalR

To establish a connection, create a HubConnectionBuilder and call the Build method. Hub URL, protocol, transport type, logging level, headers, and other options can be configured when creating a connection. Configure all required options by inserting one of the HubConnectionBuilder methods into the Build method.

Start the connection with StartAsync.

public partial class DemoSignalR
{
	private HubConnection connection;

	private string connectionUrl = "https://localhost:44391/ChatHub";
	private List<Chat> logs = new List<Chat>();
	private string message = "";
	private string userName = "UserName";

	public DemoSignalR()
	{
		// Create the new SignalR Hub
		connection = new HubConnectionBuilder()
		   .WithUrl(connectionUrl)
		   .Build();
	}

	public void Dispose()
	{
		OnClose();
	}

	private async void OnClose()
	{
		// Send message for user disconnect
		await connection.InvokeAsync("SendMessage", new Chat { Type = "disconnect", Name = userName });

		// Stop the connection
		await connection.StopAsync();
	}

	private async void OnConnect()
	{
		// Handler to treat the receive message
		connection.On<Chat>("ReceiveMessage", chat =>
		{
			logs.Add(chat);
			StateHasChanged();
		});

		// Start the connection
		await connection.StartAsync();

		// Send message for user connect
		await connection.InvokeAsync("SendMessage", new Chat { Type = "connect", Name = userName });
	}

	private async Task SendMessageAsync()
	{
		// Send the user message
		await connection.InvokeAsync("SendMessage", new Chat { Type = "message", Name = userName, Message = message });
	}
}