Axelar Example: A Simple Counter

Overview

This repository is an example of using Axelar to do cross-chain calls using interface contracts similar to the ones that Cubist will generate. The example is based on other Axelar examples.

In this simple example, there are two functions (inc() and store(uint256)) in an Ethereum contract (EthCounter) that we call from Avalanche through the Axelar infrastructure. The contracts that a user would write are EthCounter.sol (deployed on Ethereum) and AvaCounter.sol (deployed on Avalanche).

On the Avalanche side there is an EthCounter.sol contract that exposes the cross-chain functions in an interface that corresponds to the contract on the Ethereum side. The functions on this contract encode the function and arguments for the cross-chain calls, use the Axelar API to pay for the cross-chain calls, and then use the API to initiate the call. The cross-chain function to call is encoded using abi.encodeWithSignature().

On the Ethereum side there is an EthCounterInterface.sol contract that acts as the receiving contract for calls from Axelar. To do so, it overrides the _execute() function and executes the call stored in the payload on the original contract. It then matches the function id and invokes the corresponding function on the original contract with the decoded arguments.

Deployment

The deployment of the contracts in this repository has to happen in the following order:

• EthCounter on Ethereum
• EthCounterInterface on Ethereum (requires the address of (EthCounter)
• EthCounter (the interface) on Avalanche (requires the address of EthCounterInterface)
• AvaCounter on Avalanche (requires the address of the EthCounter interface)

Testing the example

Build contracts:

npm install
npx hardhat compile

Start servers (run command in a different terminal or background):

node scripts/runLocal.js

Deploy contracts:

node scripts/deploy.js

Test contracts/bridging:

node scripts/test.js