Cairo Solidity Integration Example

Install Dependencies

npm i

Set .env file

mv .env.sample .env

In .env file:

API_URL = "https://eth-goerli.alchemyapi.io/v2/your-api-key"
PRIVATE_KEY = "your-metamask-private-key"
CONTRACT_ADDRESS = "put here the address where your contract was deployed... only known after deployment"

L1 Setup

Compile L1 contracts

npx hardhat compile

Deploy your contract on Goerli test net

npx hardhat run scripts/deploy.js --network goerli

Update .env file with the contract address

Contract deployed to address: 0xCAFBf889bef0617d9209Cf96f18c850e901A6D61

Interact with your L1 smart contract

npx hardhat run scripts/interact.js

If you need more help, plese refer to https://www.web3.university/tracks/create-a-smart-contract.

L2 Setup

Compile L2

cd cairo-contracts
export STARKNET_NETWORK=alpha-goerli
starknet-compile l2.cairo --output l2_compiled.json --abi l2_abi.json

Creating and Deploying Account

export STARKNET_WALLET=starkware.starknet.wallets.open_zeppelin.OpenZeppelinAccount
starknet deploy_account

Deploy L2 Contract on testnet alpha-goerli

starknet deploy --contract l2_compiled.json
export CONTRACT_ADDRESS= <contract address>

Interacting with L2 contract

starknet invoke --address ${CONTRACT_ADDRESS} --abi l2_abi.json --function <setter function> --inputs <input separated by space>
starknet call   --address ${CONTRACT_ADDRESS} --abi l2_abi.json --function <getter function> --inputs <input separated by space>
starknet tx_status --hash <hash of the transaction>

Help

pragma solidity ^0.6.12;

interface IStarknetCore {
    function sendMessageToL2(
        uint256 toAddress,
        uint256 selector,
        uint256[] calldata payload
    ) external returns (bytes32);

    function consumeMessageFromL2(uint256 fromAddress, uint256[] calldata payload)
        external
        returns (bytes32);
}

contract L1L2Example {
    // The StarkNet core contract.
    IStarknetCore starknetCore;

    mapping(uint256 => uint256) public userBalances;

    uint256 constant MESSAGE_WITHDRAW = 0;

    // The selector of the "deposit" l1_handler.
    uint256 constant DEPOSIT_SELECTOR =
        352040181584456735608515580760888541466059565068553383579463728554843487745;

    constructor(IStarknetCore starknetCore_) public {
        starknetCore = starknetCore_;
    }

    function withdraw(
        uint256 l2ContractAddress,
        uint256 user,
        uint256 amount
    ) external {
        // Construct the withdrawal message's payload.
        uint256[] memory payload = new uint256[](3);
        payload[0] = MESSAGE_WITHDRAW;
        payload[1] = user;
        payload[2] = amount;

        // Consume the message from the StarkNet core contract.
        // This will revert the (Ethereum) transaction if the message does not exist.
        starknetCore.consumeMessageFromL2(l2ContractAddress, payload);

        // Update the L1 balance.
        userBalances[user] += amount;
    }

    function deposit(
        uint256 l2ContractAddress,
        uint256 user,
        uint256 amount
    ) external {
        require(amount < 2**64, "Invalid amount.");
        require(amount <= userBalances[user], "The user's balance is not large enough.");

        // Update the L1 balance.
        userBalances[user] -= amount;

        // Construct the deposit message's payload.
        uint256[] memory payload = new uint256[](2);
        payload[0] = user;
        payload[1] = amount;

        // Send the message to the StarkNet core contract.
        starknetCore.sendMessageToL2(l2ContractAddress, DEPOSIT_SELECTOR, payload);
    }
}