Vara ↔ Ethereum Cross-Chain Ping

CrossPing is a minimal decentralized application (dApp) example that demonstrates secure message delivery between Ethereum and Vara using the Vara ↔ Ethereum Bridge.
It is designed as a teaching and reference project, showing how a simple "Ping" message can travel across chains in both directions.

The project consists of six main components, grouped into two flows:

ETH → VARA

• eth-vara-pinger-eth — a solidity smart contract on Ethereum that initiates a ping.
• eth-vara-relayer-node — a Node.js/TypeScript relayer service forwarding messages from Ethereum to Vara.
• eth-vara-receiver-vara — a Vara program (Rust/Sails) that receives the ping.

VARA → ETH

• vara-eth-pinger-vara — a Vara program (Rust/Sails) that initiates a ping.
• vara-eth-relayer-node — a Node.js/TypeScript relayer service forwarding messages from Vara to Ethereum.
• vara-eth-receiver-eth — a solidity smart contract on Ethereum that receives the ping.

This repository serves as a minimal working cross-chain example.

It can be used by developers to:

• Understand how the Vara ↔ Ethereum Bridge works in practice.
• Experiment with sending and receiving messages across chains.
• Learn how relayers and contracts integrate into a simple end-to-end flow.

Installation

From the repository root:

pnpm install

This installs dependencies for all workspace packages.

Build

Build all JS/TS packages and all Rust projects:

pnpm build

Or separately:

pnpm build:js
pnpm build:rust

Run Relayers

• ETH → VARA:

  pnpm --filter eth-vara-relayer-node dev

• VARA → ETH:

  pnpm --filter vara-eth-relayer-node dev

Deploy and Ping (Hardhat Contracts)

• Deploy pinger on Ethereum (Holesky network):

  pnpm --filter eth-vara-pinger-eth deploy

• Send a ping from Ethereum:

  pnpm --filter eth-vara-pinger-eth ping

• Deploy receiver on Ethereum (Hoodi network):

  pnpm --filter vara-eth-receiver-eth deploy

Build Vara Programs

Rust/Sails packages are built via the root Cargo workspace:

cargo build --workspace

Or individually:

pnpm --filter eth-vara-receiver-vara build
pnpm --filter vara-eth-pinger-vara build

Run Order per Flow

Vara → Ethereum Flow

1. Deploy PingReceiver on Ethereum using Hardhat.
2. Deploy Vara Ping program (vara-eth-pinger-vara) via Gear IDEA.
   • Provide the Ethereum PingReceiver’s H160 address (20 bytes) as the initial payload.
3. Start the Vara → ETH relayer (vara-eth-relayer-node) with the proper configuration.
4. Trigger a Ping directly from Vara (via IDEA’s SendMessage).
5. With the relayer running, the Ping is delivered and processed on Ethereum.

Ethereum → Vara Flow

1. Deploy EthPinger contract on Ethereum (eth-vara-pinger-eth).
2. Deploy Vara PingReceiver program (eth-vara-receiver-vara) via Gear IDEA.
3. Start the ETH → Vara relayer (eth-vara-relayer-node) with the proper configuration.
4. Trigger a Ping by calling the ping() function in the EthPinger contract.
5. With the relayer running, the Ping is delivered and processed on Vara.