<?xml version="1.0" encoding ="utf-8"?>
　　　　　<access-policy>
    　　　　<cross-domain-access>
       　　　　 <policy>
           　　　　 <allow-from>
                　　　　<domain uri="*" />
            　　　　</allow-from>
            　　      <grant-to>
                             <socket-resource port="4502-4534" protocol="tcp" />
                             <resource path="/clientbin"/>   
                        </grant-to>
                  </policy>
                </cross-domain-access>
               </access-policy>

   internal void StartupPolicyServer()
        {
            string policyFile = Path.Combine(Application.StartupPath, "clientaccesspolicy.xml");//读取安全策略文件的内容放入policyBuffer  byte[]中

using (FileStream fs = new FileStream(policyFile, FileMode.Open, FileAccess.Read))
            {
                policyBuffer = new byte[fs.Length];
                fs.Read(policyBuffer, 0, policyBuffer.Length);
            }
            try
            {
                listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                listener.Bind(new IPEndPoint(IPAddress.Any, 943));//监听943端口
                listener.Listen(100);
                listener.BeginAccept(new AsyncCallback(OnClientConnect), null);//当客户端访问943端口时回调OnClientConnect方法
            }
            catch
            { 
            }
        }

//客户端访问943端口时

private readonly string policyRequestString = "<policy-file-request/>";

private void OnClientConnect(IAsyncResult result)
        {

....

requestBuffer = new byte[policyRequestString.Length];

client.BeginReceive(requestBuffer, 0, policyRequestString.Length, SocketFlags.None, new AsyncCallback(OnReceive), client);//接收"<policy-file-request/>"内容长度的byte[]请求。

}

//服务端开始接收客户端的数据

private void OnReceive(IAsyncResult result)
        {
            Socket client = result.AsyncState as Socket;
            try
            {
                received += client.EndReceive(result);//累加接收的字节数目，为了判断是否接收完
                if (received < policyRequestString.Length) //如果"<policy-file-request/>"内容长度的byte[]没有接收完继续接收
                {
                    client.BeginReceive(requestBuffer, received, policyRequestString.Length - received, SocketFlags.None, new AsyncCallback(OnReceive), client);
                    return;
                }
                string request = System.Text.Encoding.UTF8.GetString(requestBuffer, 0, received);
                if (StringComparer.InvariantCultureIgnoreCase.Compare(request, policyRequestString) != 0) //如果客户端在943端口发送的不是"<policy-file-request/>"内容的数据,也就是说请求的不是安全策略文件，就退出函数
                {
                    client.Close();
                    return;
                }
                client.BeginSend(policyBuffer, 0, policyBuffer.Length, SocketFlags.None, new AsyncCallback(OnSend), client);//否则就把安全策略文件的byte[]内容发送给客户端
            }

catch (SocketException)
            {
                client.Close();
            }
        }