last modified July 5, 2023
In this article we show how to work with websockets in C#.
WebSocket is a computer communications protocol, providing full-duplex communication channels over a single TCP connection. WebSockets are used in highly interactive applications such as games, chats, or stock markets.
We create an ASP.NET application with a websocket support. We create two clients: a C# console program and a HTML page with JS code.
The following is a simple websocket server application.
using System.Net;
using System.Net.WebSockets;
using System.Text;
var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();
app.UseWebSockets();
app.Map("/ws", async context =>
{
if (context.WebSockets.IsWebSocketRequest)
{
using var webSocket = await context.WebSockets.AcceptWebSocketAsync();
var rand = new Random();
while (true)
{
var now = DateTime.Now;
byte[] data = Encoding.ASCII.GetBytes($"{now}");
await webSocket.SendAsync(data, WebSocketMessageType.Text,
true, CancellationToken.None);
await Task.Delay(1000);
long r = rand.NextInt64(0, 10);
if (r == 7)
{
await webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure,
"random closing", CancellationToken.None);
return;
}
}
}
else
{
context.Response.StatusCode = (int)HttpStatusCode.BadRequest;
}
});
app.Run("http://localhost:5050");
The application sends the current datetime to the client. When the random number generator chooses value 7, we close the connection.
using System.Net.WebSockets;
Websocket support is in System.Net.WebSockets namespace.
app.UseWebSockets();
We enable websocket middleware with UseWebSockets.
app.Map("/ws", async context =>
{
We map the communication to the /ws endpoint.
if (context.WebSockets.IsWebSocketRequest)
{
We check if the request is a WebSocket establishment request.
using var webSocket = await context.WebSockets.AcceptWebSocketAsync();
We transition the request to a WebSocket connection with
AcceptWebSocketAsync.
var now = DateTime.Now;
byte[] data = Encoding.ASCII.GetBytes($"{now}");
await webSocket.SendAsync(data, WebSocketMessageType.Text, true, CancellationToken.None);
We send data to the client with SendAsync. The data is the current
datetime.
long r = rand.NextInt64(0, 10);
if (r == 7)
{
await webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure,
"random closing", CancellationToken.None);
return;
}
We randomly close the connection with CloseAsync.
$ dotnet watch
We start the server with dotnet watch.
In the next example we create a C# console program that establishes a websocket connection to the server.
using System.Net.WebSockets;
using System.Text;
Console.Title = "Client";
using var ws = new ClientWebSocket();
await ws.ConnectAsync(new Uri("ws://localhost:5050/ws"), CancellationToken.None);
byte[] buf = new byte[1056];
while (ws.State == WebSocketState.Open)
{
var result = await ws.ReceiveAsync(buf, CancellationToken.None);
if (result.MessageType == WebSocketMessageType.Close)
{
await ws.CloseAsync(WebSocketCloseStatus.NormalClosure, null, CancellationToken.None);
Console.WriteLine(result.CloseStatusDescription);
}
else
{
Console.WriteLine(Encoding.ASCII.GetString(buf, 0, result.Count));
}
}
We establish a websocket connection to the server from a console application.
using var ws = new ClientWebSocket();
The ClientWebSocket is used to create websocket clients in a C#
application.
await ws.ConnectAsync(new Uri("ws://localhost:5050/ws"), CancellationToken.None);
We asynchronously connect to the ws://localhost:5050/ws endpoint
with ConnectAsync.
byte[] buf = new byte[1056];
This is the buffer to which we read the response.
var result = await ws.ReceiveAsync(buf, CancellationToken.None);
We read the response with ReceiveAsync.
if (result.MessageType == WebSocketMessageType.Close)
{
await ws.CloseAsync(WebSocketCloseStatus.NormalClosure, null, CancellationToken.None);
Console.WriteLine(result.CloseStatusDescription);
}
else
{
Console.WriteLine(Encoding.ASCII.GetString(buf, 0, result.Count));
}
If the message type is WebSocketMessageType.Close, we close the
connection from the client side with CloseAsync and print the
closing description. Otherwise we print the received data.
$ dotnet run 10/28/2022 2:57:48 PM 10/28/2022 2:57:49 PM 10/28/2022 2:57:50 PM 10/28/2022 2:57:51 PM 10/28/2022 2:57:52 PM 10/28/2022 2:57:53 PM 10/28/2022 2:57:54 PM 10/28/2022 2:57:55 PM random closing
In the next example, we create a JS client that creates a websocket connection.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script type="text/javascript">
function connect() {
let o = document.getElementById("output");
var ws = new WebSocket("ws://localhost:5050/ws");
ws.onmessage = e => {
o.innerText = e.data;
};
ws.onclose = e => {
o.innerText = e.reason;
};
};
</script>
</head>
<body>
<div id="output">
</div>
<p>
<a href="#" onclick="connect()">Start</a></div>
</p>
</body>
</html>
In JS, we use the WebSocket class and the onmessage and
onclose handlers.
WebSocket class - language reference
In this article we have worked with WebSocket in C#.
My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.
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