You must also update the read / write position of the stream by the number of bytes that were successfully written.
This method is called in response to fread() and fgets() calls on the stream. You must return up-to count bytes of data from the current read/write position as a string. If there are less than count bytes available, return as many as are available. If no more data is available, return either FALSE or an empty string. You must also update the read/write position of the stream by the number of bytes that were successfully read.