How to implement Websocket AP?

ICSM Computer 490 10 Dec 2025

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Updated 10 Dec 2025

1 Answers

ICSM Computer 10 Dec 2025

What Is a WebSocket API?

A WebSocket API lets the browser and server stay connected with a persistent two-way connection.

HTTP → Request → Response → Connection CLOSED
WebSocket → OPEN connection → send/receive anytime

Perfect for:

Real-time chat
Notifications
Live dashboards
Online games
Stock/price tickers

1. Implement WebSocket in JavaScript (Client)

let socket = new WebSocket("ws://localhost:5000/ws/chat");

socket.onopen = function () {
    console.log("Connected to server");
    socket.send("Hello server!");
};

socket.onmessage = function (event) {
    console.log("Message from server:", event.data);
};

socket.onclose = function () {
    console.log("Connection closed");
};

socket.onerror = function (err) {
    console.error("WebSocket error", err);
};

// Send message
function sendMessage(msg) {
    if (socket.readyState === WebSocket.OPEN) {
        socket.send(msg);
    }
}

2. ASP.NET Core WebSocket Server (Recommended)

(MVC 5 does NOT support WebSockets directly.)

Startup.cs

public void Configure(IApplicationBuilder app)
{
    app.UseWebSockets();

    app.Use(async (context, next) =>
    {
        if (context.Request.Path == "/ws/chat")
        {
            if (context.WebSockets.IsWebSocketRequest)
            {
                var socket = await context.WebSockets.AcceptWebSocketAsync();
                await Echo(socket);
            }
            else
            {
                context.Response.StatusCode = 400;
            }
        }
        else
        {
            await next();
        }
    });
}

private async Task Echo(WebSocket socket)
{
    var buffer = new byte[1024 * 4];
    var result = await socket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);

    while (!result.CloseStatus.HasValue)
    {
        var msg = Encoding.UTF8.GetString(buffer, 0, result.Count);

        // Send message back
        await socket.SendAsync(
            Encoding.UTF8.GetBytes("Server: " + msg),
            WebSocketMessageType.Text,
            true,
            CancellationToken.None
        );

        result = await socket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
    }

    await socket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
}

This is a minimal production-ready WebSocket API.

Which One Should YOU Use?

Technology	Use When
ASP.NET Core WebSockets	You are using .NET Core or .NET 6+
SignalR (MVC 5)	You are using .NET Framework MVC 5
Pure WebSocket	You need full control, low-level protocol

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