using System;
using System.Net.WebSockets;
using System.Threading.Tasks;
using System.Web;
using System.Web.WebSockets;

namespace WebSocketTest
{
    public class MyWebSocketHandler : IHttpHandler
    {
        /// <summary>
        /// 设置实例不可以重复使用
        /// </summary>
        public bool IsReusable
        {
            get
            {
                return false;
            }
        }

        /// <summary>
        /// 判断是否是WebSocket请求
        /// 是交由handlerWebSocketAsync方法处理
        /// </summary>
        /// <param name="context"></param>
        public void ProcessRequest(HttpContext context)
        {
            if (context.IsWebSocketRequest)
            {
                context.AcceptWebSocketRequest(handlerWebSocketAsync);
            }
        }

        private async Task handlerWebSocketAsync(AspNetWebSocketContext context)
        {
            WebSocket webSocket = context.WebSocket;

            await webSocket.SendMsgAsync("连接成功");

            while (true)
            {
                if (webSocket.State == WebSocketState.Open)
                {
                    string msg = await webSocket.ReceiveMsgAsync();
                    webSocket.SendMsgAsync(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")
                        + @",Receive:" + msg);
                }
            }
        }
    }
}

using System;
using System.Net.WebSockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace WebSocketTest
{
    public static class WebSocketHelper
    {
        /// <summary>
        /// 发送消息
        /// </summary>
        /// <param name="webSocket"></param>
        /// <param name="msg"></param>
        /// <returns></returns>
        public static async Task SendMsgAsync(this WebSocket webSocket, string msg)
        {
            byte[] bytesMsg = Encoding.UTF8.GetBytes(msg);
            ArraySegment<byte> segment = new ArraySegment<byte>(bytesMsg);
            await webSocket.SendAsync(segment, WebSocketMessageType.Text, true, CancellationToken.None);
        }

        /// <summary>
        /// 接收消息
        /// </summary>
        /// <param name="webSocket"></param>
        /// <returns></returns>
        public static async Task<string> ReceiveMsgAsync(this WebSocket webSocket)
        {
            ArraySegment<byte> receiveSegment = new ArraySegment<byte>(new byte[1024]);
            WebSocketReceiveResult receiveResult = await webSocket.ReceiveAsync(receiveSegment, CancellationToken.None);

            string clientMsg = Encoding.UTF8.GetString(receiveSegment.Array, 0, receiveResult.Count);
            return clientMsg;
        }
    }
}

<system.web>
    <compilation debug="true" targetFramework="4.6.1"/>
    <httpRuntime targetFramework="4.5"/>
    <!--<httpHandlers>
      <add verb="*" path="*" type="WebSocketTest.MyWebSocketHandler, WebSocketTest" />
    </httpHandlers>-->
  </system.web>
  <system.webServer>
    <handlers>
      <add name="webSocketHandler" verb="*" path="*" type="WebSocketTest.MyWebSocketHandler, WebSocketTest"/>
    </handlers>
  </system.webServer>