AXFR is a TCP-only operation (RFC 5936), but the request handler did
not enforce that. When a UDP datagram carrying an AXFR query arrived,
control reached _handle_axfr_request, which builds the multi-message
response and writes each chunk with:
self.request.sendall(len(wire).to_bytes(2, 'big') + wire)
For a UDP handler self.request is a (data, sock) tuple, not a socket,
so sendall raised AttributeError. The exception was caught by the
outer try/except in UDPRequestHandler.handle, so the server stayed up,
but the client received no response at all and the error was only
visible in a generic 'Error handling request' traceback.
Add a 'transport' class attribute ('tcp' / 'udp') to the concrete
handler classes and, immediately after the qtype check (before TSIG
validation and zone lookup), deny AXFR-over-UDP with REFUSED. The
client now gets a proper refusal and the AXFR handler is never entered
on a UDP socket.
Sven Luethi
0277063dcc