FIX: CInternet::File ReadString() Loses Data

SYMPTOMS

Calling CInternetFile::ReadString() without calling SetReadBufferSize() first can result in lost data. If the file being read is less than 4096 bytes (the default read buffer size), a null string will be returned into the buffer specified by the first argument of ReadString(). The ReadString() function will also return NULL. If the file being read is greater than 4096 bytes, the first 4096 bytes will be lost and then subsequent ReadString() calls will return the rest of the data.

You can see this problem by running the TEAR MFC sample that is included on the Visual C++ 4.2 CD.

   if (m_pbReadBuffer == NULL)
   {
       if (!SetReadBufferSize(4096))   // arbitrary but reasonable
           return NULL;
       if (!InternetReadFile(m_hFile, m_pbReadBuffer, m_nReadBufferSize,
               &dwRead))
           AfxThrowInternetException(m_dwContext);
        m_nReadBufferBytes = dwRead;
   }
				

   TCHAR sz[1024];
   pFile->SetReadBufferSize(4096);  // Add this line
   while (pFile->ReadString(sz, 1023))
   {
       if (bStripMode)
       StripTags(sz);
       cout << sz;
   }