This implementation is incorrect. The loops currently exits when a packet is fully parsed, and the stream can continue.
Your implementation makes the stream "dirty". It stops in the middle of the parsing of a packet and another call to fetch_one would return an error. The current implementation does not.

Also, fetch_one is not a main loop. It fetches one packet, and parses it. The main loop should be in your code.

"main loop" would be in the __iter__ if you use BinLogStreamReader as an iterator (github does not show comment in context if you do not change this line)