Frontier is Substrate's Ethereum compatibility layer. It allows you to run unmodified Ethereum dapps.

The goal of Ethereum compatibility layer is to be able to:

• Run a normal web3 application via the compatibility layer, using local nodes, where an extra bridge binary is acceptable.
• Be able to import state from Ethereum mainnet.

It consists of the following components:

• pallet-evm: EVM execution engine for Substrate.
• pallet-ethereum: Emulation of full Ethereum block processing.
• rpc-ethereum: Compatibility layer for web3 RPC methods.

Frontier is still work-in-progress. Below are some notes about the development.

A few notes on the EthereumRuntimeApi's runtime implementation requirements:

• For supporting author rpc call, the FindAuthor trait must be implemented in an arbitrary struct. This implementation must call the authorities accessor in either Aura or Babe and convert the authority id response to H160 using pallet_evm::HashTruncateConvertAccountId::convert_account_id.

The struct implementing FindAuthor is passed as the FindAuthor associated type's value for pallet_ethereum.

An Aura example for this is available in the template's runtime (EthereumFindAuthor).

• For supporting chain_id rpc call, a u64 ChainId constant must be defined.

• For supporting gas_price rpc call, FeeCalculator trait must be implemented in an arbitrary struct. An example FixedGasPrice is available in the template's runtime.

1. Override your local cargo config to point to your local substrate (pointing to your WIP branch): place paths = ["path/to/substrate"] in ~/.cargo/config.
2. You are good to go.

Remember to comment out the override after it is done to avoid mysterious build issues on other repo.