size -= m_lastcount;
buf = (char *)buf + m_lastcount;
- // the call to wxStreamBuffer::Read() below will reset our m_lastcount,
- // so save it
+ // the call to wxStreamBuffer::Read() below may reset our m_lastcount
+ // (but it also may not do it if the buffer is associated to another
+ // existing stream and wasn't created by us), so save it
size_t countOld = m_lastcount;
- m_i_streambuf->Read(buf, size);
+ // the new count of the bytes read is the count of bytes read this time
+ m_lastcount = m_i_streambuf->Read(buf, size);
+ // plus those we had read before
m_lastcount += countOld;
}