Interact with EVM smart contracts

This is a simple dApp to show how one can trigger smart contract functions on an EVM base layer from a Cartesi rollup. In this example, our application logic resides on two layers - the EVM base layer and the Cartesi execution layer.

• On base layer - We deploy a simple contracts/Storage.sol smart contract on our local Anvil node and try to hit its store() function. This dApp logic is further extended by deploying contracts/SimpleERC721.sol contract to trigger mint() function.
• On Cartesi execution layer - With the logic inside src/index.js, you can set the address of the previously deployed smart contracts and parse input JSON to check user input for either storing a number or minting an NFT.

Running the backend

Pre-requisite: Cartesi CLI and Docker desktop

Build the Cartesi backend

cartesi build

Run the backend node

cartesi run --epoch-duration 30

Deploy solidity smart contracts

You can choose a method of your choice to compile and deploy the contracts inside ./contracts directory. We'll use Remix IDE here.

• Open Remix online and create a new workspace.

• Copy Storage.sol from ./contracts and paste in contracts folder on your Remix workspace.

• Compile the contract using Ctrl+S

• Before deploying, make sure you have local Anvil network added to Metamask and few accounts imported for testing. You can follow the answer here to set this up.

• To deploy - Connect the Injected Provider - Metamask in Environment and select an imported account as a deployer. Hit deploy.

• Save address of the deployed contract to use later.
• You can follow the same steps to deploy the NFT contract or any other custom solidity smart contract.

Sending inputs to the Cartesi backend

To send inputs we can use below command on a separate terminal tab.

cartesi send generic

When prompted for an input JSON string, refer the following samples.

To relay the address of your deployed smart contracts:

{"method": "set_address", "address": "your-contract-address-here"}

Create voucher to generate a number to store on base layer:

{"method": "generate_number", "number": "7"}

Create voucher mint an NFT:

{"method": "mint_nft"}

Executing vouchers

This step finally triggers the base layer functions. Open below url in your browser.

http://localhost:8080/explorer

Look for the voucher created against your latest inputs in the local rollups explorer. In the explorer, every voucher gives you an execute button to trigger the desired on-chain action.

Reading base layer

You can use cast command in terminal to read the updated value on Storage contract.

cast call <deployed-contract-address-here> "retrieve()(uint256)" 0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266 --mnemonic "test test test test test test test test test test test junk" --mnemonic-index 0 --rpc-url "http://localhost:8545"

If everything went well, above command will give you twice the number you sent as an input. That's all for this tutorial. Bye!