We propose to add transferShares function into the stETH contract which accepts shares amount as input and performs shares movement from one account to another. We also propose to add event TransferShares which must be emitted along with Transfer event. We propose that calling transferShares(recipient, sharesAmt) should lead to exactly the same outcome as calling transfer(recipient, sharesAmt * sharePrice). Including that both transferShares and transfer should emit TransferShares and Transfer events. The only difference being the measurement unit of the input amount.
Full specification and pull request with contracts changes can be found in lido-improvement-proposals repository.
Motivation
stETH is a rebasing token. Usually, we transfer stETH using ERC-20 transfer and transferFrom functions which accept as input amount of stETH, not the amount of the underlying shares.
Sometimes we’d better operate with shares directly to avoid possible rounding issues (the first clear example is LIP-6 proposal, see recoverExcessStETH). Rounding issues usually could appear after a token rebase.
Backward compatibility
We preserve the existing Transfer event signature cause it’s defined by ERC-20. That’s why we introduce the new TransferShares event instead of adding another arg for the existing Transfer event.
Gas price effects
Emitting the TransferShares event costs approximately 1900 additional gas, depending on the execution context.
Transfer of stETH
An addition of emitting the TransferShares event increases the cost of every stETH transfer (call to Lido contract’s transfer(...)) by ~3.6% (1967 gas).
Submitting ETH to Lido contract
Gas price of submitting ETH for minting stETH is also affected because on minting we need to emit TransferShares(address(0), ...) as well as Transfer(address(0), ...) event.
Slight 1891 gas (~2.2%) increase in costs for every call to the Lido contract’s submit(...) function.
Handling LidoOracle report
Call to LidoOracle’s reportBeacon which leads to consensus will emit 2 + N TransferShares events, where N is the amount of Node Operators stored in the registry (14 at the moment). Thus, cost of calling reportBeacon will increase by ~30000 gas which is ~6%. The cost is paid approximately every day on a beacon chain state report by the Oracle who reports by calling reportBeacon “the last”. It happens to be 0x007DE4a5F7bc37E2F26c0cb2E8A95006EE9B89b5 these days.