Ftp文件传输完成后，为什么接收不到完成后server发送的命令信息？

[Ack_001]

我在做的一个Ftp文件传输工具，在文件下载过程中发生了奇怪的现象，小弟百思不解，故向各位大哥请教！小弟先谢了！！！
问题如下：
在文件下载过程中，当文件较小时（小于15M）程序正常没有任何异常；但是但文件稍大时，如：30M。这时候文件能够 完成下载，下载后文件大小根ftp服务器上文件大小一样，但是就是接收不到ftp服务器返回的下载成功信息。<调试中发现，程序阻塞在接受ftp命令消息处...>导致程序卡在那里了！

各位大哥，多多指教哈！
主要代码为：

//------------------------------ SocketTcp 类------------------------------//
class  SocketTCP
{
public :
    SocketTCP();
    void SetBlocking(bool Blocking);
    Socket::Status Connect(unsigned short Port, const IPAddress& HostAddress, float Timeout = 0.f);
    bool Listen(unsigned short Port);
    Socket::Status Accept(SocketTCP& Connected, IPAddress* Address = NULL);
    Socket::Status Send(const char* Data, std::size_t Size);
    Socket::Status Receive(char* Data, std::size_t MaxSize, std::size_t& SizeReceived);
    bool Close();          // 关闭套接字
    bool IsValid() const;  // 验证套接字是否有效
    bool operator ==(const SocketTCP& Other) const;
    bool operator !=(const SocketTCP& Other) const;
    bool operator <(const SocketTCP& Other) const;
private :
    friend class Selector<SocketTCP>;
    SocketTCP(SocketHelper::SocketType Descriptor);
    void Create(SocketHelper::SocketType Descriptor = 0);
	// 成员变量
    SocketHelper::SocketType mySocket;            ///< Socket descriptor
    Uint32                   myPendingHeader;     ///< Data of the current pending packet header, if any
    Uint32                   myPendingHeaderSize; ///< Size of the current pending packet header, if any
    std::vector<char>        myPendingPacket;     ///< Data of the current pending packet, if any
    Int32                    myPendingPacketSize; ///< Size of the current pending packet, if any
    bool                     myIsBlocking;        ///< Is the socket blocking or non-blocking ?
};

//---------------------------------Ftp 类--------------------------------------//
class SFML_API Ftp : NonCopyable
{
public :
    enum TransferMode
    {
        Binary, ///< Binary mode (file is transfered as a sequence of bytes)
        Ascii,  ///< Text mode using ASCII encoding
        Ebcdic  ///< Text mode using EBCDIC encoding
    };
	// ---------------------------报文类----------------------------------------//
    class Response
    {
    public :
        enum Status
        {
            // 枚举的报文常量，就没列出来了
        };
        Response(Status Code = InvalidResponse, const std::string& Message = "");
        bool IsOk() const;
        Status GetStatus() const;
        const std::string& GetMessage() const;

    private :
        Status      myStatus;  ///< Status code returned from the server
        std::string myMessage; ///< Last message received from the server
    };
	// 其他成员函数就没列举出来了，不然太长了
	Ftp(bool translateMode = false);
    ~Ftp();
    Response Download(const std::string& DistantFile, const std::string& DestPath, TRANSLATEINFO* pTransInfo = NULL, TransferMode Mode = Binary);
    Response Upload(const std::string& LocalFile, const std::string& DestPath, TransferMode Mode = Binary);

private:
    Response SendCommand(const std::string& Command, const std::string& Parameter = "");
    Response GetResponse();
    class DataChannel;
    friend class DataChannel;
    SocketTCP myCommandSocket; ///< Socket holding the control connection with the server>
};

//----------------------------------DataChannel 类----------------------------------//
class Ftp::DataChannel : NonCopyable
{
public :
    DataChannel(Ftp& Owner);
    ~DataChannel();
    Ftp::Response Open(Ftp::TransferMode Mode);
    void Send(const std::vector<char>& Data);
    void Receive(std::vector<char>& Data);
	bool RecevieFile(std::string &filename, DWORD filesize, TRANSLATEINFO* pTransInfo = NULL);	
private :
    Ftp&      myFtp;        ///< Reference to the owner Ftp instance
    SocketTCP myDataSocket; ///< Socket used for data transfers
	SocketTCP FtpCommandSocket; ///< Ftp command socket>
	CallBackShowSpeed cbShowSpeed;   ///回调函数指针变量
};

// 文件下载函数
Ftp::Response Download(const std::string& DistantFile, const std::string& DestPath, TRANSLATEINFO* pTransInfo, TransferMode Mode)
{
    // Open a data channel using the given transfer mode
    DataChannel Data(*this);           // 打开数据通道，接收数据《DataChannel是'数据类'》
    Response Resp = Data.Open(Mode);   /*Response 是'ftp报文类'，记录命令通道返回的命令消息*/
    if (Resp.IsOk())                   // 命令通道返回的信息表示数据通道连接成功
    {
		// Get the remote file size
		Ftp::FileInfoResponse ResSize = GetFileSize(DistantFile);
		std::string remoteStr = ResSize.GetFileInfo();
		DWORD dwRometeSize    = atol(remoteStr.c_str());
        // Tell the server to start the transfer
        Resp = SendCommand("RETR", DistantFile);
        if (Resp.IsOk())               
        {
			// Extract the filename from the file path
			std::string Filename = DistantFile;
            std::string::size_type Pos = Filename.find_last_of("/\\");
            if (Pos != std::string::npos)
                Filename = Filename.substr(Pos + 1);			
            // Make sure the destination path ends with a slash
            std::string Path = DestPath;
            if (!Path.empty() && (Path[Path.size() - 1] != '\\') && (Path[Path.size() - 1] != '/'))
                Path += "/";
			Path += Filename;
            if (!Data.RecevieFile(Path, dwRometeSize, pTransInfo))				
			   return Response(Response::InvalidFile); //error
			Resp = GetResponse();      /*程序就卡在这一步了*/《获取完成下载后，命令通道返回的信息》
        }
    }
    return Resp;
}
// 从命令通道获取报文方法
Ftp::Response Ftp::GetResponse()
{
    for (;;)
    {
        char Buffer[1024];
        std::size_t Length;		
		// 调试中，发现阻塞在Receive()这里了！！！(myCommandSocket是Ftp类的命令通道套接字类对象)
        if (myCommandSocket.Receive(Buffer, sizeof(Buffer), Length) != sf::Socket::Done) 
		{
            return Response(Response::ConnectionClosed); 
		}	
		
		// 消息处理...
	}
}
// 命令通道接收文件函数
bool Ftp::DataChannel::RecevieFile(std::string &filename, DWORD filesize, TRANSLATEINFO* pTransInfo)
{
	// Receive data
    char Buffer[1024] = {0};
    std::size_t Received = 0;
	DWORD size = filesize;
	float receivedSpeed = 0.0f;
	// Create file in local computer
	std::ofstream localfile(filename.c_str(), std::ios_base::binary);
	if (!localfile)
        return false;
	while (myDataSocket.Receive(Buffer, sizeof(Buffer), Received) == sf::Socket::Done)
    {
		size -= Received;
		localfile.write(Buffer, static_cast<int>(Received));
		localfile.flush();
		memset(Buffer, 0, sizeof(Buffer));
		receivedSpeed = 100*((filesize-size)/static_cast<double>(filesize));
		cbShowSpeed(filename, receivedSpeed, pTransInfo);
	}
	// Closed the localfile
	localfile.close();
    myDataSocket.Close();
	return true;
}
// 套接字接收数据函数
Socket::Status SocketTCP::Receive(char* Data, std::size_t MaxSize, std::size_t& SizeReceived)
{
    // First clear the size received
    SizeReceived = 0;
    // Check that socket is valid
    if (!IsValid())
        return Socket::Error;
    // Check parameters
    if (Data && MaxSize)
    {
        // Receive a chunk of bytes
        int Received = recv(mySocket, Data, static_cast<int>(MaxSize), 0);
        // Check the number of bytes received
        if (Received > 0)
        {
            SizeReceived = static_cast<std::size_t>(Received);
            return Socket::Done;
        }
        else if (Received == 0)
        {		
            return Socket::Disconnected;
        }
        else
        {			
            return SocketHelper::GetErrorStatus();
        }
    }
    else
    {
        // Error...
        std::cerr << "Cannot receive data from the network (invalid parameters)" << std::endl;
        return Socket::Error;
    }
}

[Ack_001]

决定修改代码格式，重传！

//------------------------------ SocketTcp 类------------------------------//
class  SocketTCP
{
public :
    SocketTCP();
    void SetBlocking(bool Blocking);
    Socket::Status Connect(unsigned short Port, const IPAddress& HostAddress, float Timeout = 0.f);
    bool Listen(unsigned short Port);
    Socket::Status Accept(SocketTCP& Connected, IPAddress* Address = NULL);
    Socket::Status Send(const char* Data, std::size_t Size);
    Socket::Status Receive(char* Data, std::size_t MaxSize, std::size_t& SizeReceived);
    bool Close();          // 关闭套接字
    bool IsValid() const;  // 验证套接字是否有效
    bool operator ==(const SocketTCP& Other) const;
    bool operator !=(const SocketTCP& Other) const;
    bool operator <(const SocketTCP& Other) const;
private :
    friend class Selector<SocketTCP>;
    SocketTCP(SocketHelper::SocketType Descriptor);
    void Create(SocketHelper::SocketType Descriptor = 0);
// 成员变量
    SocketHelper::SocketType mySocket;  ///< Socket descriptor
    Uint32 myPendingHeader;             ///< Data of the current pending packet header, if any
    Uint32 myPendingHeaderSize;         ///< Size of the current pending packet header, if any
    std::vector<char> myPendingPacket;  ///< Data of the current pending packet, if any
    Int32                    myPendingPacketSize; ///< Size of the current pending packet, if any
    bool                     myIsBlocking;        ///< Is the socket blocking or non-blocking ?
};

//---------------------------------Ftp 类--------------------------------------//
class SFML_API Ftp : NonCopyable
{
public :
    enum TransferMode
    {
        Binary, ///< Binary mode (file is transfered as a sequence of bytes)
        Ascii,  ///< Text mode using ASCII encoding
        Ebcdic  ///< Text mode using EBCDIC encoding
    };
// ---------------------------报文类----------------------------------------//
    class Response
    {
    public :
        enum Status
        {
            // 枚举的报文常量，就没列出来了
        };
        Response(Status Code = InvalidResponse, const std::string& Message = "");
        bool IsOk() const;
        Status GetStatus() const;
        const std::string& GetMessage() const;
    private :
        Status      myStatus;  ///< Status code returned from the server
        std::string myMessage; ///< Last message received from the server
    };
    // 其他成员函数就没列举出来了，不然太长了
    Ftp(bool translateMode = false);
    ~Ftp();
    Response Download(const std::string& DistantFile, const std::string& DestPath,
                     TRANSLATEINFO* pTransInfo = NULL, TransferMode Mode = Binary);
    Response Upload(const std::string& LocalFile, const std::string& DestPath, 
                    TransferMode Mode = Binary);     
private:
    Response SendCommand(const std::string& Command, const std::string& Parameter = "");
    Response GetResponse();
    class DataChannel;
    friend class DataChannel;
    SocketTCP myCommandSocket; ///< Socket holding the control connection with the server>
};

//----------------------------------DataChannel 类----------------------------------//
class Ftp::DataChannel : NonCopyable
{
public :
    DataChannel(Ftp& Owner);
    ~DataChannel();
    Ftp::Response Open(Ftp::TransferMode Mode);
    void Send(const std::vector<char>& Data);
    void Receive(std::vector<char>& Data);
    bool RecevieFile(std::string &filename, DWORD filesize, TRANSLATEINFO* pTransInfo = NULL);	
private :
    Ftp& myFtp;                      ///< Reference to the owner Ftp instance
    SocketTCP myDataSocket;          ///< Socket used for data transfers
    SocketTCP FtpCommandSocket;      ///< Ftp command socket>
    CallBackShowSpeed cbShowSpeed;   ///回调函数指针变量
};

// 文件下载函数
Ftp::Response Download(const std::string& DistantFile, const std::string& DestPath, TRANSLATEINFO* pTransInfo, TransferMode Mode)
{
    // Open a data channel using the given transfer mode
    DataChannel Data(*this);           // 打开数据通道，接收数据《DataChannel是'数据类'》
    Response Resp = Data.Open(Mode);   /*Response 是'ftp报文类'，记录命令通道返回的命令消息*/
    if (Resp.IsOk())                   // 命令通道返回的信息表示数据通道连接成功
    {
	// Get the remote file size
	Ftp::FileInfoResponse ResSize = GetFileSize(DistantFile);
	std::string remoteStr = ResSize.GetFileInfo();
	DWORD dwRometeSize    = atol(remoteStr.c_str());
        // Tell the server to start the transfer
        Resp = SendCommand("RETR", DistantFile);
        if (Resp.IsOk())               
        {
	    // Extract the filename from the file path
	    std::string Filename = DistantFile;
            std::string::size_type Pos = Filename.find_last_of("/\\");
            if (Pos != std::string::npos)
                Filename = Filename.substr(Pos + 1);			
            // Make sure the destination path ends with a slash
            std::string Path = DestPath;
            if (!Path.empty() && (Path[Path.size() - 1] != '\\')
                  && (Path[Path.size() - 1] != '/'))
            {
                Path += "/";
            }
	    Path += Filename;
            if (!Data.RecevieFile(Path, dwRometeSize, pTransInfo))				
	          return Response(Response::InvalidFile); //error
	    Resp = GetResponse();  /*程序就卡在这一步了*/《获取完成下载后，命令通道返回的信息》
        }
    }
    return Resp;
}
// 从命令通道获取报文方法
Ftp::Response Ftp::GetResponse()
{
    for (;;)
    {
        char Buffer[1024];
        std::size_t Length;		
	// 调试中，发现阻塞在Receive()这里了！！！(myCommandSocket是Ftp类的命令通道套接字类对象)
        if (myCommandSocket.Receive(Buffer, sizeof(Buffer), Length) != sf::Socket::Done) 
	{
            return Response(Response::ConnectionClosed); 
	}	
		
	// 消息处理...
    }
}
// 命令通道接收文件函数
bool Ftp::DataChannel::RecevieFile(std::string &filename, DWORD filesize, TRANSLATEINFO* pTransInfo)
{
    // Receive data
    char Buffer[1024] = {0};
    std::size_t Received = 0;
    DWORD size = filesize;
    float receivedSpeed = 0.0f;
    // Create file in local computer
    std::ofstream localfile(filename.c_str(), std::ios_base::binary);
    if (!localfile)
        return false;
    while (myDataSocket.Receive(Buffer, sizeof(Buffer), Received) == sf::Socket::Done)
    {
	size -= Received;
	localfile.write(Buffer, static_cast<int>(Received));
	localfile.flush();
	memset(Buffer, 0, sizeof(Buffer));
	receivedSpeed = 100*((filesize-size)/static_cast<double>(filesize));
	cbShowSpeed(filename, receivedSpeed, pTransInfo);
    }
    // Closed the localfile
    localfile.close();
    myDataSocket.Close();
    return true;
}
// 套接字接收数据函数
Socket::Status SocketTCP::Receive(char* Data, std::size_t MaxSize, std::size_t& SizeReceived)
{
    // First clear the size received
    SizeReceived = 0;
    // Check that socket is valid
    if (!IsValid())
        return Socket::Error;
    // Check parameters
    if (Data && MaxSize)
    {
        // Receive a chunk of bytes
        int Received = recv(mySocket, Data, static_cast<int>(MaxSize), 0);
        // Check the number of bytes received
        if (Received > 0)
        {
            SizeReceived = static_cast<std::size_t>(Received);
            return Socket::Done;
        }
        else if (Received == 0)
        {		
            return Socket::Disconnected;
        }
        else
        {			
            return SocketHelper::GetErrorStatus();
        }
    }
    else
    {
        // Error...
        std::cerr << "Cannot receive data from the network (invalid parameters)" << std::endl;
        return Socket::Error;
    }
}

[Ack_001]

第一次发帖，发现格式太乱了。看来要注意了，不过小弟，新手，望各位大哥海涵了