怎么我通过FTP下载的文件要小点,帮忙看看问题出在哪儿了?

函数如下:
DownloadFile(HINTERNET hSession, LPCTSTR localFile)
{
HINTERNET hSession, LPCTSTR localFile
         HANDLE hFile;
BYTE pBuf[TRANSFER_SIZE];
DWORD dwReadSizeOut=0;
DWORD dwTotalReadSize = 0; hFile = CreateFile(localFile, GENERIC_WRITE, FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile == INVALID_HANDLE_VALUE) return FALSE;

DWORD dwWriteSize, dwNumWritten;
do { BOOL bRead = InternetReadFile(hSession, pBuf, 4096, &dwReadSizeOut);
dwWriteSize = dwReadSizeOut; if (bRead && dwReadSizeOut > 0) 
{
dwTotalReadSize += dwReadSizeOut;
WriteFile(hFile, pBuf, dwWriteSize, &dwNumWritten, NULL); 
// File write error
if (dwWriteSize != dwNumWritten)
{
CloseHandle(hFile);
return FALSE;
}
}
else {
if (!bRead)
{
// Error
CloseHandle(hFile);
return FALSE;
}
break;
}
} while(1);
CloseHandle(hFile);
return TRUE;
}