Thread: WSASend & WSARecv :: Winsock

Hi.

I am implementing a send and receive part of a simple message program. Everything seems to work okay, except the send and receive are not in sync.

For send, I use WSASend. I first send a "header" buffer with the same of the real data buffer. Next, I send the real data buffer.

For receive, I use WSARecv. I first receive the "header" buffer and determine its DWORD size. I then allocate a character array of that size. Next, I receive the real data buffer based on the size.

The problem is the "header" buffer I receive does not hold the correct data size. For example, let say the data size is 10 byte (10 characters). Instead of 10, I will get something at least in 90+ when I cast the "header" to a DWORD.

Here is the sample code for both send and receive. Please keep me updated if you find any known problem.

-----
char *data = new char[4];
data = "test";
DWORD bufferSize = static_cast<DWORD>(strlen(data)), sentSize = 0;
WSABUF bufferHDR,
bufferDATA;
char *header = new char[4];
CString sizeCnt;
sizeCnt.Format("%d", bufferSize);
strcpy(header, static_cast<LPCTSTR>(sizeCnt));
bufferHDR.len = 4;
bufferHDR.buf = header;

// sending first data buffer contain the size

if (WSASend(socket, &bufferHDR, 1, &sentSize, MSG_OOB, 0, 0) == 0)
{
bufferDATA.len = bufferSize;
bufferDATA.buf = data;
sentSize = 0;
DWORD bufferProgress = 0;

// make sure all data gets sent
while (sentSize < bufferSize)
{
if (WSASend(m_ActiveSocket, &bufferDATA, 1, &bufferProgress, MSG_OOB, 0, 0) == 0)
{
sentSize += bufferProgress;
bufferProgress = 0;
}

else
{
DetermineErrorWSASend();
sentSize = bufferSize;
}
}

else
DetermineErrorWSASend();
-----

-----
DWORD bufferSize = 0,
receivedSize = 0,
flags = 0;
WSABUF bufferHDR,
bufferDATA;
char *header = new char[4], *data;
bufferHDR.len = 4;
bufferHDR.buf = header;


// reading first buffer to determine real data size
if (WSARecv(socket, &bufferHDR, 1, &receivedSize, &flags, 0, 0) == 0)
{
CString x;
bufferSize = static_cast<DWORD>(*bufferHDR.buf);
x.Format("%s%d", "bufferSize = ", bufferSize);
AfxMessageBox(x);

// allocating memory based on buffer size

data = new char[bufferSize];
bufferDATA.len = bufferSize;
bufferDATA.buf = data;
receivedSize = 0;
DWORD bufferProgress = 0;

// make sure all buffer get read

while (receivedSize < bufferSize)
{
if (WSARecv(socket, &bufferDATA, 1, &bufferProgress, &flags, 0, 0) == 0)
{
x.Format("%d", bufferProgress);
AfxMessageBox(x);
newData += *bufferDATA.buf;
receivedSize += bufferProgress;
}

else
{
DetermineErrorWSARecv();
receivedSize = bufferSize;
}
}
delete [] data;
delete [] header;
}
-----

Thanks,
Kuphryn