78 lines
3.2 KiB
Markdown
78 lines
3.2 KiB
Markdown
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# Concepts
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## EVM
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The Ethereum Virtual Machine [EVM](https://ethereum.org/en/developers/docs/evm/) is a state machine
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that provides the necessary tools to run or create a contract on a given state.
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## State DB
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The `StateDB` interface from geth represents an EVM database for full state querying of both
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contracts and accounts. The concrete type that fulfills this interface on Ethermint is the
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`CommitStateDB`.
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## State Object
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A `stateObject` represents an Ethereum account which is being modified.
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The usage pattern is as follows:
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* First you need to obtain a state object.
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* Account values can be accessed and modified through the object.
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## Genesis State
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The `x/evm` module `GenesisState` defines the state necessary for initializing the chain from a previous exported height.
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+++ https://github.com/cosmos/ethermint/blob/v0.3.1/x/evm/types/genesis.go#L14-L20
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### Genesis Accounts
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The `GenesisAccount` type corresponds to an adaptation of the Ethereum `GenesisAccount` type. Its
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main difference is that the one on Ethermint uses a custom `Storage` type that uses a slice instead
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of maps for the evm `State` (due to non-determinism), and that it doesn't contain the private key
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field.
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It is also important to note that since the `auth` and `bank` SDK modules manage the accounts and
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balance state, the `Address` must correspond to an `EthAccount` that is stored in the `auth`'s
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module `AccountKeeper` and the balance must match the balance of the `EvmDenom` token denomination
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defined on the `GenesisState`'s `Param`. The values for the address and the balance amount maintain
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the same format as the ones from the SDK to make manual inspections easier on the genesis.json.
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+++ https://github.com/cosmos/ethermint/blob/v0.3.1/x/evm/types/genesis.go#L22-L30
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### Transaction Logs
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On every Ethermint transaction, its result contains the Ethereum `Log`s from the state machine
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execution that are used by the JSON-RPC Web3 server for for filter querying. Since Cosmos upgrades
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don't persist the transactions on the blockchain state, we need to persist the logs the EVM module
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state to prevent the queries from failing.
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`TxsLogs` is the field that contains all the transaction logs that need to be persisted after an
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upgrade. It uses an array instead of a map to ensure determinism on the iteration.
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+++ https://github.com/cosmos/ethermint/blob/v0.3.1/x/evm/types/logs.go#L12-L18
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### Chain Config
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The `ChainConfig` is a custom type that contains the same fields as the go-ethereum `ChainConfig`
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parameters, but using `sdk.Int` types instead of `*big.Int`. It also defines additional YAML tags
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for pretty printing.
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The `ChainConfig` type is not a configurable SDK `Param` since the SDK does not allow for validation
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against a previous stored parameter values or `Context` fields. Since most of this type's fields
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rely on the block height value, this limitation prevents the validation of of potential new
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parameter values against the current block height (eg: to prevent updating the config block values
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to a past block).
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If you want to update the config values, use an software upgrade procedure.
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+++ https://github.com/cosmos/ethermint/blob/v0.3.1/x/evm/types/chain_config.go#L16-L45
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### Params
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See the [params](07_params.md) document for further information about parameters.
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