Skip to content

Latest commit

 

History

History
72 lines (53 loc) · 2.99 KB

lip-9.md

File metadata and controls

72 lines (53 loc) · 2.99 KB
Raw
lip title status author discussions-to created updated
9
Add an explicit log for the stETH burn events
Implemented
Eugene Mamin, Artyom Veremeenko
2022-01-24
2022-06-06

Add an explicit log for the stETH burn events

Simple summary

Add a dedicated event to log the burnShares function invocation backing the on-chain storage state change which incurs stETH token rebase (all token holders get their balances increased).

Abstract

We propose to include SharesBurnt event into the StETH contract and emit the proposed event on every burnShares invocation. It would allow to complete off-chain logs and hold a new invariant for Lido: every stETH rebase must be covered with the some explicitly emitted event.

Motivation

Burning of the stETH underlying shares is one of the on-chain effects causing stETH token rebase. We'd like to have all token rebases logged. It's a good thing to have in general. In particular, it would allow not to miss a rebase for the off-chain interactive UIs and to sync on-chain storage change with 3rd-party off-chain indexers and monitoring.

Specification

Every token rebase caused by shares burning must emit SharesBurnt event indicating the caller account, burnt shares amount and the corresponding amount of tokens burnt.

New SharesBurnt event

We propose to include SharesBurnt event into the StETH contract having the following signature:

    /**
     * @notice An executed `burnShares` request
     *
     * @dev Reports simultaneously burnt shares amount
     * and corresponding stETH amount.
     * The stETH amount is calculated twice: before and after the burning incurred rebase.
     *
     * @param account holder of the burnt shares
     * @param preRebaseTokenAmount amount of stETH the burnt shares corresponded to before the burn
     * @param postRebaseTokenAmount amount of stETH the burnt shares corresponded to after the burn
     * @param sharesAmount amount of burnt shares
     */
    event SharesBurnt(
        address indexed account,
        uint256 preRebaseTokenAmount,
        uint256 postRebaseTokenAmount,
        uint256 sharesAmount
    );

New version of the burnShares function

Cause the burning also decreases the total amount of minted shares, the balance of the account will be decreased by a different amount, so we need to calculate a pre/post token amount. So there are 3 new lines to add:

uint256 preRebaseTokenAmount = getPooledEthByShares(_sharesAmount);
...
uint256 postRebaseTokenAmount = getPooledEthByShares(_sharesAmount);

emit SharesBurnt(_account, preRebaseTokenAmount, postRebaseTokenAmount, _sharesAmount);

Gas price effects

Negligible: stETH burning is expected to happen no more than a few times per year, extra event costs are negligible.

Links

The proposed change for the StETH contract can be found in PR linked to this issue.