A prototype of EXIT stable token

See https://poa.gitbook.io/exit/ first to get the detailed info of the concept.

Contracts

This prototype consists of three contracts:

• Reward is a main contract which emulates a rewardable action (in this case - finishing staking epoch and minting EXIT tokens) and implements the rebalance mechanism of SoftETH tokens total supply. This contract is upgradeable by the RewardProxy contract. For upgradability we use OpenZeppelin solution.

• ExitToken is an ERC20 token contract representing EXIT token. It is mintable by the Reward contract. Initially, it's created with an empty supply. The supply is increased by the Reward.finishStakingEpoch() function (see below). No one else can mint the EXIT tokens.

• SoftETHToken is an ERC20 token contract representing SoftETH token. It is mintable and burnable by the Reward contract. Initially, it's created with an empty supply. The supply is changed by the Reward.rebalance() function (see below). No one else can mint or burn the SoftETH tokens.

These contracts are deployed in Ethereum Mainnet (see addresses). We use a public price oracle contract available on Mainnet to retrieve the current ETH/USD rate.

For ERC20 implementations we use the latest OpenZeppelin contracts.

Reward contract constants

These constants are supposed to be unchanged during prototype's life:

• COLLATERAL_MULTIPLIER defines how many times the USD worth of SoftETH tokens must exceed the total supply of EXIT tokens. It's equal to 2.

• EXIT_MINT_RATE defines the percent rate of how many EXIT tokens must be minted in relation to the USD worth of STAKE tokens totally staked. It's defined as 10%.

Reward contract setters

The Reward contract contains three setters:

1. finishStakingEpoch accepts totalStakeAmount as a single parameter and emulates finishing of staking epoch. The totalStakeAmount defines the total amount of STAKE tokens staked by the moment of staking epoch end. This parameter is used along with STAKE/USD rate and EXIT_MINT_RATE to calculate the amount of EXIT tokens needed to be minted as a reward. The function mints EXIT tokens and calls the rebalance function. finishStakingEpoch can be called by anyone at any time.

2. rebalance rebalances the totalSupply of SoftETH tokens so that it would exceed EXIT token supply COLLATERAL_MULTIPLIER times in USD worth. This function doesn't accept any parameters and can be called by anyone at any time.

3. setSTAKEUSD sets the current STAKE/USD rate in USD cents (for example, 10 USD would be 1000). Can only be called by an address named Currency Rate Changer (see below).

Reward contract getters

There are a few public getters which could be helpful:

• ethUsdCurrent returns the current amount of USDTs in 1 ETH (in USD cents) provided by the price oracle. The returned value has 2 decimals.

• usdEthCurrent returns the current amount of ETHs in 1 USDT (i.e. USDT/ETH rate) provided by the price oracle. The returned amount has 18 decimals.

• exitCurrentSupply returns the current total supply of EXIT tokens.

• softETHCurrentSupply returns the current total supply of SoftETH tokens.

• softETHExpectedSupply returns the current expected supply of SoftETH tokens based on the current supply of EXIT tokens, COLLATERAL_MULTIPLIER, and the current USDT/ETH rate.

• ethUsd returns the latest known ETH/USD rate (in USD cents) set by rebalance function. The returned amount has 2 decimals.

• stakeUsd returns the STAKE/USD rate set by setSTAKEUSD function. The returned amount has 2 decimals.

The Reward contract is well documented, so you can look into its code and get the detailed information about each function.

The ABIs are available in etherscan.io as the contracts are verified (see contract addresses).

User roles

The Reward contract assumes to have three users:

1. Proxy admin who can upgrade the code of the Reward contract through the RewardProxy contract. The proxy admin cannot call Reward functions.

2. Staker is an arbitrary address which receives minted EXIT tokens. The Staker emulates the staking of STAKE tokens (as a single staker in the system). When the Reward.finishStakingEpoch function is called (by any address) with a non-zero totalStakeAmount parameter, it's supposed that the staker had staked totalStakeAmount STAKE tokens before staking epoch finished. This prototype doesn't have STAKE token contract - the tokens are only emulated by the Reward.finishStakingEpoch function.

3. Currency Rate Changer is an address that is allowed to call the Reward.setSTAKEUSD function. For simplicity, we assume this address is the same as Staker.

Contracts deployment on Ethereum Mainnet

1. Clone the repo and initialize it:

   $ git clone https://github.com/xdaichain/exit-reward-prototype
   $ cd exit-reward-prototype
   $ npm i

2. Create keys file in the root of the repo which should contain private keys for the admin and staker/currencyRateChanger addresses (one line for each).

   Example of the keys file content (the first is for the admin, the second is for staker/currencyRateChanger):

   123a...bc45
   678d...ef90
   

   The admin address cannot be the same as staker/currencyRateChanger.

   Make sure the admin address has at least 0.02 ETH and the staker/currencyRateChanger has at least 0.001 ETH (for the gasPrice of 5 gwei).

3. Set appropriate gasPrice in truffle-config.js (the default is 5 gwei).

4. Launch the deployment script as follows:

   $ env STAKEUSD=1000 npm run deploy -- --network mainnet # STAKEUSD is STAKE/USD rate in USD cents

If the deployment is successful, you will see addresses.mainnet.json file in the root of the repo. The file will contain all addresses needed to work with this prototype (contract addresses; admin, staker, currencyRateChanger).

Usage

To emulate the minting of EXIT tokens, call the Reward.finishStakingEpoch function. This function cannot be called by the admin, so please use another address for making the transaction. To ensure the supply of EXIT tokens is increased, use exitToken.totalSupply getter.

To rebalance SoftETH supply after ETH/USD rate changing, call Reward.rebalance. This function cannot be called by the admin, so please use another address for making the transaction.

To change STAKE/USD rate, call the Reward.setSTAKEUSD function by the Currency Rate Changer address.

To compare the current SoftETH supply with the expected supply, use Reward.softETHCurrentSupply and Reward.softETHExpectedSupply getters. They should return almost the same value after rebalance is called.

To know the current ETH/USD rate provided by the price oracle, use Reward.ethUsdCurrent getter.

UI

The Application for interaction with the contracts is available in the app directory.