Comment 13 for bug 1572719

It's been awhile since I looked at this but IIRC the ChunkWriteTimeout triggers a GeneratorExit or two in proxy_logging middleware and probably _get_response_parts_iter. I can't quite remember the call sequence, but that leads to wsgi trying to close the client socket and triggering the flush.

When I used wsgi.server(..., socket_timeout=30, ...) a socket.timeout was thrown but still didn't close the socket which was why I suggested the finally block.