Use cases for reentry

[leighmcculloch]

Hi all! There's been some discussion in Discord and elsewhere about reentry. It'd be helpful to have a good understanding of how reentry would be used if the feature was added.

Please post a new top-level comment in this discussion for each use case reentry would have. Be as detailed as possible in explaining why reentry is needed for that use case.

This discussion thread is not about any specific reentry proposal. For reentry proposals, please start a new discussion. This discussion thread is just a place to collect use cases.

[kalepail]

I'm working on smart wallets and we have the concept of policy signers which are separate contracts which execute as a cross contract call from within the smart wallet's __check_auth method. It would be nice from within the policy to be able to call back to the smart wallet to read in at least get methods for reading contract data like signer info if not also being able to do full writes for modifying the smart wallet itself. Currently this isn't possible and the only real work around is passing a lot of info in via arguments which can make it difficult then to filter and operate conditionally on.

And there's no work around for modifying the smart wallet itself from within the policy during a policy invocation from the smart wallet

[leighmcculloch]

For the read only data requests could the wallet make two calls to the policy signer, first asking for a list of data, then making the final call with the accompanying data?

Doing the two steps may in some cases be more efficient than calling back N times. Unless the data required is dependent on the values returned.

[leighmcculloch]

For the modifications to the policy could the policy pass them back in the return value?

[kalepail]

could the wallet make two calls to the policy signer

Hmm...maybe? I hadn't thought about this route. But probably?? It's backwards to what you'd expect to do but likely a sufficient work around, especially given the limited and standard things a policy could potentially request from a wallet

for the modifications to the policy could the policy pass them back in the return value?

Also possibly. Again a bit backwards to what you'd expect but could definitely work I think

I'll do some exploring. Thanks!

[jayz22]

The most typical example is one of flash loan, where a borrower calls into a liquidity pool making a loan and the pool calls the borrower contract back to perform some custom logic (before returning the loan), all within the same invocation atomically.

Tagging @esteblock and @rudewalt who have requested it in the original tracking issue stellar/rs-soroban-env#336

[andreas-osec]

In flash loans, the invoker doesn’t necessarily need to be the borrowing contract - in fact, it typically isn’t. In such scenarios, reentrancy isn’t required. The xycloans implementation is good example of this approach