app.UseWebSockets();

app.UseWebSockets(new WebSocketOptions()
{
    KeepAliveInterval = TimeSpan.FromSeconds(120),
    ReceiveBufferSize = 4 * 1024
});

async Task WebSocketMiddleware(HttpContext context, Func<Task> next)
{
    //這里監(jiān)聽的是 /ws 作為地址
    if (context.Request.Path != "/ws")
    {
        await next();
        return;
    }
                                                                                        
    if (!context.WebSockets.IsWebSocketRequest)
    {
        context.Response.StatusCode = 400;
        return;
    }

    WebSocket webSocket = await context.WebSockets.AcceptWebSocketAsync();
    await Echo(context, webSocket);
}

app.Use(WebSocketMiddleware);

async Task Echo(HttpContext context, WebSocket webSocket)
{
    var buffer = new byte[1024 * 4];
    WebSocketReceiveResult result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
    while (!result.CloseStatus.HasValue)
    {
        await webSocket.SendAsync(new ArraySegment<byte>(buffer, 0, result.Count), 
　　　　　　　　　　result.MessageType, result.EndOfMessage, CancellationToken.None);
        result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
    }
    await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
}