c#socket双向通信，收不到服务器的反馈信息

请问大神们：为什么c#socket通信时，同步的，客户端必须先收到服务器的应答，才开始发送数据，但是在服务器收到数据处理完后，反馈给客户端时为什么收不到了？

服务器代码：
namespace serverfile
{
public partial class Form1 : Form
{

    string fileaddr = @"C:\Documents and Settings\Administrator\桌面\filetr\serverfile\recv.xml";
    private Socket server = null;
    private Socket client = null;

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {

        //创建EndPoint
        IPAddress ipAddress = IPAddress.Parse("127.0.0.1");
        IPEndPoint endpoint = new IPEndPoint(ipAddress, 7000);
        //创建socket
        if (server == null)
        {
            server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            server.Bind(endpoint);
        }
        else
        {
        }
    }

    private void button2_Click(object sender, EventArgs e)
    {
        Control.CheckForIllegalCrossThreadCalls = false;
        Thread TempThread = new Thread(new ThreadStart(this.StartReceive));
        TempThread.Start();
    }
    private void StartReceive()
    {
       // IPEndPoint ipep = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 7000);
       // Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
       // server.Bind(ipep);
        while (true)
        {
            server.Listen(10);
            client = server.Accept();

            string str = "连接成功";
            byte[] clientString = Encoding.Default.GetBytes(str);
            client.Send(clientString);



            EndPoint tempRemoteEP = client.RemoteEndPoint;
            IPEndPoint tempRemoteIP = (IPEndPoint)tempRemoteEP;
            //获取请求的远程计算机名称
            string remoteIP = tempRemoteIP.Address.ToString();
            label1.Text = "连接状态：已经连接！";

            FileStream MyFileStream = new FileStream(fileaddr, FileMode.Create, FileAccess.Write);
            byte[] data = new byte[2048];
            int sent=0;
            while (true)
            {
                sent=client.Receive(data);
                if (sent == 0)
                {
                    break;
                }
                else
                {
                    // SendedCount++;
                    MyFileStream.Write(data, 0, sent);
                }
            }
            MyFileStream.Close();

            xmlread(client );
            client.Close();

        }

    }

    public void xmlread(Socket s)
    {
        XmlDocument doc = new XmlDocument();
        //   doc.Load(@"D:\Csharp\xmlread\CKECKINFO_Device_id_1.xml");    //加载Xml文件 
        doc.Load(fileaddr);    //加载Xml文件
        // 得到根节点bookstore
        XmlNode xn = doc.SelectSingleNode("info");
        // 得到根节点的所有子节点
        XmlNodeList xnl = xn.ChildNodes;
        string str = "";
        foreach (XmlNode xn1 in xnl)
        {
            // 将节点转换为元素，便于得到节点的属性值
            XmlElement xe = (XmlElement)xn1;
            str = str + "user_id" + xe.GetAttribute("user_id").ToString();
            // 得到Book节点的所有子节点
            XmlNodeList xnl0 = xe.ChildNodes;
            str = str + ";" + xnl0.Item(0).InnerText;
            str = str + ";" + xnl0.Item(1).InnerText;
            str = str + ";" + xnl0.Item(2).InnerText;
            str = str + ";" + xnl0.Item(3).InnerText;
            str = str + ";" + xnl0.Item(4).InnerText;
        }
        MessageBox.Show(str);


        string str1 = "接收成功";
        byte[] clientString1 = Encoding.Default.GetBytes(str1);
        s.Send(clientString1);

        File.Delete(fileaddr);
    }




}

}

客户端代码：
namespace clientfile
{

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        Thread TempThread = new Thread(new ThreadStart(this.StartSend));
        TempThread.Start();
    }
    private void StartSend()
    {
        //FileInfo EzoneFile = new FileInfo(this.textBox1.Text);

        string path = @"C:\Documents and Settings\Administrator\桌面\filetr\clientfile\CKECKINFO_Device_id_1.xml";

        FileInfo EzoneFile = new FileInfo(path);
        FileStream EzoneStream = EzoneFile.OpenRead();

        int PacketSize = 2048;
        int PacketCount = (int)(EzoneStream.Length / ((long)PacketSize));
        int LastDataPacket = (int)(EzoneStream.Length - ((long)(PacketSize * PacketCount)));
        IPEndPoint ipep = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 7000);
        Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

        client.Connect(ipep);
        byte[] data = new byte[PacketSize];
        for (int i = 0; i < PacketCount; i++)
        {
            EzoneStream.Read(data, 0, data.Length);
            TransferFiles.SendVarData(client, data);
        }

        if (LastDataPacket != 0)
        {
            data = new byte[LastDataPacket];
            EzoneStream.Read(data, 0, data.Length);
            TransferFiles.SendVarData(client, data);
           // MessageBox.Show("client,data.length" + Convert.ToString(data.Length));
        }

        EzoneStream.Close();

        Receive(client );


        client.Close();
    }

    public void Receive(Socket s)
    {
        byte[] res = new byte[100];

        s.Receive(res);

        MessageBox.Show(Encoding.Default.GetString(res));
    }
}


class TransferFiles
{

    public TransferFiles()
    {

    }

    public static int SendVarData(Socket s, byte[] data) // return integer indicate how many data sent.
    {
        int total = 0;
        int size = data.Length;
        int dataleft = size;
        int sent;

        while (total < size)
        {
            sent = s.Send(data, total, dataleft, SocketFlags.None);
            total += sent;
            dataleft -= sent;
        }

        return total;
    }

Server的StartReceive里面的处理有误。

你在while循环**后**发送反馈，就是那个xmlread(client )。
但是，你的while循环只会在客户关闭socket连接的时候才退出，因此客户不能接收到你的反馈。

具体来说，while循环里面，你判断send==0的情况下退出循环(注：这里的send是错字，英文应该用received)。
但是根据MSDN参考，send==0意味着客户关闭连接。