Overview

A Layer Zero Rate Provider that allows the LST conversion rate to be bridged across networks. This rate provider will support the launch of Balancer on Polygon zkEVM. This review covers the compatibility of the RateProvider, the cross-chain price update mechanism, as well as the deployed contract code for RateProvider (Mainnet) and RateReceiver (Polygon zkEVM).

Repo

https://github.com/witherblock/gyarados

Contract Scope

**[RateProvider](<https://github.com/witherblock/gyarados/blob/main/contracts/CrossChainRateProvider.sol>)**

• Provides an exchange rate to the RateReceiver contract on a different chain than the origin blockchain using a LayerZeroEndpoint.
• A user must manually “poke” this contract once daily to continuously update the rate.
  • updateRate

**[RateReceiver](<https://github.com/witherblock/gyarados/blob/main/contracts/CrossChainRateReceiver.sol>)**

• Receives the exchange rate from the RateProvideron a different chain than the corresponding RateProvider.
• Utilizes the LayerZeroReceiver.
• The pool will consume the rate using getRate.

Contract Reviews

RateProvider

• The contract name needs to be more specific since it is being used only for wstETH.
• Why is there one instance of this contract for each child chain? Seems wasteful. Proposed change:
  • array of chainIds
  • mapping(uint256 →address) (chainId →rateReceiver)
  • on updateRate(), iterate through all chainIds, and send to LZEndpoint
• LOW — There are currently no comments explaining why updateRate is payable.
  • From our review of LayerZero contracts, it is clear that this function is payable in order to pay protocol fees, and payments to the oracle and relayer.
  • This explanation needs to be added as well as the necessary value of ETH to send.
• LOW — add token getter, base asset getter
• LOW — have a constructor that sets an initial state
• MEDIUM - add reentrancy guards for the updateRate function.