C＃套接字接收：套接字缓冲区上的“接收”不会覆盖现有的套接字缓冲区内容

Question

我正在使用自定义的客户端服务器套接字应用程序传输文件。传输过程分为多个阶段，文件本身分为多个块（每个块为4K大小）。 所以，这就是问题所在。输入套接字缓冲区不会被新的块覆盖，而只会继续追加到现有的块中。

以下是我的部分客户代码。服务器代码很好，因为已经存在用C ++编写的客户端代码。我正在用C＃重写客户端。套接字连接没有问题。 任何帮助都会很棒。提前致谢。

Socket _clientSocket = null; 
bool GetFile()
{
    // _strIPAddress and _nPortNumber are already assigned to valid data
    IPAddress _ipAddress; 
    if (IPAddress.TryParse(_strIPAddress, out _ipAddress) == false)         
        return false;

    IPEndPoint _serverEP = new IPEndPoint(_ipAddress, _nPortNumber);
    _clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.IP);
    _clientSocket.Connect(_serverEP);

    // socket connected, now inform server to send the file, by sending opcode 
    if (SendOperationCommand() == false)
        return false;

    // size is received properly
    if (recv_size() == false)
        return false;

    **// the first chunk of file data received, does not overwrite the socket buffer and thus, 
    // when read, it contains the previous data i.e, the file size!**
    if (recv_file() == false)
        return false;

    return true; 
}

bool SendOperationCommand()
{
    ...
    ...
    // put my operation command in the buffer and send it using the following 
    bytesSent = _clientSocket.Send(cmd, (int)BufferSize.BUFF_SIZE_OPCODE, SocketFlags.None);
    if(bytesSent <= 0)
        return false; 
    return true;
}

bool recv_size()
{
    _clientSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, (int)Timers.TIMEOUT_SIZE); 
    try
    {
        bytesReceived = _clientSocket.Receive(sizeBuffer, (int)BufferSize.BUFF_FILE_SIZE, SocketFlags.None);
    }
    catch (SocketException socEx)
    {       
        return false; 
    }

    // file size received 
    ...

    return true; 
}

bool recv_file()
{
    ...
    ...

    _clientSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, (int)Timers.TIMEOUT_FILE); 
    try
    {
        ***// the 'fileBuff' here has the file size read previously!!!!!
        bytesReceived = _clientSocket.Receive(fileBuff, (int)BufferSize.BUFF_FILE_SIZE, SocketFlags.None);***
    }
    catch (SocketException socEx)
    {       
        return false; 
    }

    // file size received 
    ...

    return true; 
}