Check if Tor clients sometimes send duplicate cells on rendezvous circuits: Possible replay detected! An INTRODUCE2 cell with thesame ENCRYPTED section was seen

As my v3 onion service is getting more and more popular, I started to get:

[warn] Possible replay detected! An INTRODUCE2 cell with thesame ENCRYPTED section was seen 32 seconds ago. Dropping cell.

I am inclined to think that this is more like a bug in Tor, maybe due to a race condition, rather than a replay attack.

I also think this is what causes legacy/trac#15618 (moved) - dgoulet confirmed that the warning can be reproduced every time a second ESTABLISH_RENDEZVOUS is sent over the same circuit.

This can probably go away if we fix legacy/trac#21084 (moved). I am not sure if that should be a parent ticket here or not, please change if you feel like it. I think I still have yawning's tool and notes about how to reproduce legacy/trac#21084 (moved).