laconicd/x/evm/spec/02_state.md

State

The x/evm module keeps the following objects in state:

	Key	Value
Block Height	[]byte{1} + []byte(block.Hash)	BigEndian(block.Height)
Bloom	[]byte{2} + []byte(block.Height)	[]byte(Bloom)
Tx Logs	[]byte{3} + []byte(tx.Hash)	amino([]Log)
Account Code	[]byte{4} + []byte(code.Hash)	[]byte(Code)
Account Storage	[]byte{5} + []byte(address) + []byte(state.Key)	[]byte(state.Value)
Chain Config	[]byte{6}	amino(ChainConfig)

CommitStateDB

StateDBs within the ethereum protocol are used to store anything within the IAVL tree. StateDBs take care of caching and storing nested states. It's the general query interface to retrieve contracts and accounts

The Ethermint CommitStateDB is a concrete type that implements the EVM StateDB interface. Instead of using a trie and database for querying and persistence, the CommitStateDB uses KVStores (key-value stores) and Cosmos SDK Keepers to facilitate state transitions.

The CommitStateDB contains a store key that allows the DB to write to a concrete subtree of the multistore that is only accessible to the EVM module.

+++ https://github.com/cosmos/ethermint/blob/v0.3.1/x/evm/types/statedb.go#L33-L85

The functionalities provided by the Ethermint StateDB are:

• CRUD of stateObjects and accounts:
  • Balance
  • Code
  • Nonce
  • State
• EVM module parameter getter and setter
• State transition logic
  • Preparation: transaction index and hash, block hash
• CRUD of transaction logs
• Aggregate queries
• Snapshot state
  • Identify current state with a revision
  • Revert state to a given revision
• State transition and persistence
  • Preparation: tx and block context
  • Commit state objects
  • Finalise state objects
  • Export state for upgrades
• Auxiliary functions
  • Copy state
  • Reset state

State Objects

State objects are used by the VM which is unable to deal with database-level errors. Any error that occurs during a database read is memoized here and will eventually be returned by StateDB.Commit.

The Ethermint stateObject is a concrete type that mimics the functionality from the go-ethereum private stateObject type. It keeps track of the interim values for the contract bytecode, storage state and balance of an EthAccount.

The storage entries (original and "dirty") for each state object are represented as slices instead of maps since latter can cause non-deterministic block app hashes, which result in the chain halting.

When a stateObject is committed during EndBlock. It sets sets the account contract code to store, as well as the dirty storage state. The account's nonce and the account balance are updated by calling the auth and bank module setter functions, respectively.

+++ https://github.com/cosmos/ethermint/blob/v0.3.1/x/evm/types/state_object.go#L49-L81

The functionalities provided by the Ethermint stateObject are:

• Storage state getter and setter (temporary)
• Contract bytecode getter and setter (temporary)
• Balance getter and setter (temporary)
• Balance accounting (temporary)
• Account nonce and address getter and setter (temporary)
• Auxiliary functions: copy, RLP encoding, empty
• Commit state object (final)