laconicd/x/evm/spec/05_abci.md

ABCI

The Application Blockchain Interface (ABCI) allows the application to interact with the Tendermint Consensus engine. The application maintains several separate ABCI connections with Tendermint. The most relevant for the x/evm is the Consensus connection at Commit. This connection is responsible for block execution and calls the fuctions InitChain (containing InitGenesis), BeginBlock, DeliverTx, EndBlock, Commit . InitChain is only called the first time a new blockchain is started and DeliverTx is called for each transaction in the block.

InitGenesis

InitGenesis initializes the EVM module genesis state by setting the GenesisState fields to the store. In particular it sets the parameters and genesis accounts (state and code).

ExportGenesis

The ExportGenesis ABCI function exports the genesis state of the EVM module. In particular, it retrieves all the accounts with their bytecode, balance and storage, the transaction logs, and the EVM parameters and chain configuration.

BeginBlock

The EVM module BeginBlock logic is executed prior to handling the state transitions from the transactions. The main objective of this function is to:

• Set the context for the current block so that the block header, store, gas meter, etc are available to the Keeper once one of the StateDB functions are called during EVM state transitions.
• Set the EIP155 ChainID number (obtained from the full chain-id), in case it hasn't been set before during InitChain

EndBlock

The EVM module EndBlock logic occurs after executing all the state transitions from the transactions. The main objective of this function is to:

• Emit Block bloom events
  • This is due for Web3 compatibility as the Ethereum headers contain this type as a field. The JSON-RPC service uses this event query to construct an Ethereum Header from a Tendermint Header.
  • The block Bloom filter value is obtained from the Transient Store and then emitted