2.6 KiB
Concepts
EVM Gas Denom
In order to use the EVM and be compatible with existing clients, the gas denom used by the EVM must be in 18 decimals. Since ukava has 6 decimals of precision, it cannot be used as the EVM gas denom directly.
To use the Kava token on the EVM, the evmutil module provides an EvmBankKeeper that is responsible for the conversion of ukava and akava. A user's excess akava balance is stored in the x/evmutil store, while its ukava balance remains in the cosmos-sdk x/bank module.
EvmBankKeeper Overview
The EvmBankKeeper provides access to an account's total akava balance and the ability to transfer, mint, and burn akava. If anything other than the akava denom is requested, the EvmBankKeeper will panic.
This keeper implements the x/evm module's BankKeeper interface to enable the usage of akava denom on the EVM.
x/evm Parameter Requirements
Since the EVM denom akava is required to use the EvmBankKeeper, it is necessary to set the EVMDenom param of the x/evm module to akava.
Balance Calculation of akava
The akava balance of an account is derived from an account's spendable ukava balance times 10^12 (to derive its akava equivalent), plus the account's excess akava balance that can be accessed via the module Keeper.
akava <> ukava Conversion
When an account does not have sufficient akava to cover a transfer or burn, the EvmBankKeeper will try to swap 1 ukava to its equivalent akava amount. It does this by transferring 1 ukava from the sender to the x/evmutil module account, then adding the equivalent akava amount to the sender's balance in the module state.
In reverse, if an account has enough akava balance for one or more ukava, the excess akava balance will be converted to ukava. This is done by removing the excess akava balance in the module store, then transferring the equivalent ukava coins from the x/evmutil module account to the target account.
The swap logic ensures that all akava is backed by the equivalent ukava balance stored in the module account.
ERC20 token <> sdk.Coin Conversion
x/evmutil enables the conversion between ERC20 tokens and sdk.Coins. This done through the use of the MsgConvertERC20ToCoin & MsgConvertCoinToERC20 messages (see Messages).
Only ERC20 contract address that are whitelist via the EnabledConversionPairs param (see Params) can be converted via these messages.
Module Keeper
The module Keeper provides access to an account's excess akava balance and the ability to update the balance.