Submitted by cmichel
The users fulfill signature on the receiving chain is at the same time used by the router as a way to claim their amount on the sending chain.
If the sending chains expiry date has passed, the user can cancel this side of the transfer and claim back their deposit before the router can claim it.
Therefore, the comment that the receiving chains expiry needs to be decreased is correct:
However, this is not enforced and if a wrong expiry date is chosen by the router, or the sender congests the network long enough such that the routers fulfill transaction does not get through, the router loses their claim and the user gets a free cross-chain transfer.
It would be possible to enforce that receivingSide.expiry + buffer < sendingSide.expiry if the original expiry was part of the invariant data.
This would programmatically avoid errors like the ones mentioned. (Assuming all supported chains use the same way to measure time / use UNIX timestamps.)
LayneHaber (Connext) acknowledged:
