[CHECKLIST] ETH2 light client on substrate using Rainbow Bridge

[drewstone]

Overview

The main checklist for tracking what needs to get done to get this working.

Components

1. Pallet
2. Types libraries (pulled from lighthouse / rainbow-bridge
3. Relayer service (pulled from rainbow-bridge, using webb-relayer)
4. Substrate client lib to interact with pallet (subxt)

Tasks

• Pallet scaffold
• Pallet preliminary tests
• Pallet no_std/wasm compilation in a substrate node runtime.
• Implement EthClientPalletTrait for EthClientPallet (used to interface with pallet from relayer)
• Integrate Eth2SubstrateRelay into a LightClientRelayer service using our relayer software.
• [TASK] Test relayer libraries w/ pallet directly using a mocked runtime #22
• Integration test relayer w/ local chain with pallet-eth2-light-client and subxt
• Stable subxt, pallet, relayer dependencies
• Pallet built and tested (continue updating against any changes to rainbow-bridge)
• Light client relayer crates building and tested (continue updating against any changes to eth2near-relay)

Mock testing

Testing pallet in Substrate usually starts with unit tests against a mocked runtime. You can find the mocked runtime for the light client inside the pallet directly, https://github.com/webb-tools/pallet-eth2-light-client/blob/drew/relay/pallet/src/mock.rs. Specifically, the mocked runtime has a user-defined struct such as Eth2Client that can be manipulated to interact with the pallet's API directly.

For mocked testing, we would likely import the eth2substrate-block-relay-rs library into the pallet as a dev-dependency and then run the relayer in the pallet testing environment.

Integration testing

Testing the pallet as an integration test will require integrating it into a full Substrate node. This testing setup will require running a live node adjacent to the relayer/tests of the relayer. Integration testing should only be done using subxt which is the library for making remote calls to a Substrate chain.