Deploy a contract with Foundry

Any smart contract deployable to the Ethereum network can be deployed easily to the Polygon zkEVM network. In this guide, we demonstrate how to deploy an ERC-721 token contract on the Polygon zkEVM network using Foundry.

We follow the Soulbound NFT tutorial from this video.

Set up the environment¶

Foundry is a smart contract development toolchain. It can be used to manage dependencies, compile a project, run tests and deploy smart contracts. It also lets one interact with the blockchain from the CLI or via Solidity scripts.

Install Foundry¶

If you have not installed Foundry, Go to book.getfoundry and select Installation from the side menu. Follow the instructions to download Using Foundryup.

Next, select Creating a New Project from the sidebar. Initialize and give your new project a name: forge init zkevm-sbt

In case of a library not loaded error, you should run below command and then repeat the above process again:

brew install libusb

If you never installed Rust or need an update, visit the website here.

Build a project and test¶

Run the command forge build to build the project. The output should look something like this:

Successful forge build command

Now, test the build with forge test

Testing Forge Build

You can check out the contents of the newly built project by switching to your IDE. In case of VSCode, just type: code .

Writing the smart contract¶

Find the OpenZeppelin Wizard in your browser, and use the wizard to create an out-of-the-box NFT contract.
- Select the ERC721 tab for an NFT smart contract.
- Name the NFT and give it an appropriate symbol. Example: Name SoEarly and Symbol SOE.
- Go ahead and select features for your token. Simply tick the relevant boxes.
- You can tick the URI Storage box if you wish to attach some image or special text to the token.
Open your CLI and install dependencies with this command:
```
npm install @openzeppelin/contracts-upgradeable
```
Remap dependencies to easy-to-read filenames with the command:
```
forge remappings > remappings.txt
```
Inside the new remapping.txt file, rename the referencing openzeppelin-contracts to openzeppelin, which is the name used when importing. That is, change openzeppelin-contracts/=lib/openzeppelin-contracts → openzeppelin/=lib/openzeppelin-contracts.
Copy the smart contract code in OpenZeppelin: Copy to Clipboard
In the IDE, open a new .sol file, name it and paste the copied code to this file. This is in fact the actual smart contract for the NFT.

Add control on token transfers¶

The aim here is to put rules in place stipulating that the token cannot be transferred without burning it.

Go to the OpenZeppelin documentation.
Look up the signature by searching for _beforetokentransfererc721.

Scroll down to ERC 721 and copy the corresponding text on the right side:

_beforeTokenTransfer(address from, address to, uint256 firstTokenId, uint256 batchSize) internal

Create a new function in the code for the smart contract token called _beforeTokenTransfer

function _beforeTokenTransfer (address from, address to, uint256 firstTokenId, uint256 batchSize) internal override {
    require(from==address(0) || to==address(0), "Soulbound: cannot transfer");
    super._beforeTokenTransfer(from, to, firstTokenId, batchSize);
}

Set a token URI (optional)¶

A token URI is a function that returns the address where the metadata of a specific token is stored. The metadata is a . json file where all the data associated with the NFT is stored. Our aim here is to attach some image to the created token.

The stored data typically consists of the name of the token, brief description and URL where the image is stored.

Choose an image and give it a name relatable to the token
Find an IPFS storage service for the image, for example filebase or web3.storage that provide free options, or NFT.storage flagship product that charge a one-time fee per GB of storage.
Upload the image to the storage using your GitHub account

Add URI json file¶

This is the file that contains the metadata for the token which includes the image address (i.e., the IPFS address of the image).

In the IDE, create a new .json file which you can call tokenuri.json

Populate the tokenuri.json file with the token-name, description and URL where the image is stored:

{
    "title": "So Early",
    "description": "I was super duper early to the Polygon zkEVM",
    "image": "<IPFS address>" /* remove the forward-slash at the end of the URL, if any */
}

Upload the tokenuri.json file to the same storage where the image was uploaded
Copy the address to the Sbt.sol inside the safeMint function
Remove the uri parameter so as to hardcode it. This results in all minted tokens sharing the same uri image, but each token’s tokenId differs from the previous one by 1.

Populate the `.env` file¶

In order to deploy on the zkEVM Testnet, populate the .env file in the usual way. That is,

Create a .env.sample file within the src folder
Populate .env.sample file with your ACCOUNT_PRIVATE_KEY and the zkEVM Testnet’s RPC URL found here. So the .env.sample file looks like this:
```
RPC_URL="https://rpc.cardona.zkevm-rpc.com"
PVTKEY="<insert private key here>"
```
Copy the contents of the .env.sample file to the .env file,
```
cp .env.sample .env
```

Warning

Make sure .env is in the .gitignore file to avoid uploading your ACCOUNT_PRIVATE_KEY.

Deploy your contract¶

In the CLI, use the following command to ensure grabbing variables from .env:
```
source .env
```
Check if the correct RPC URL is read from the .env file:
```
echo $RPC_URL
```
You can now use the next command:
```
forge create --rpc-url $RPC_URL --private-key $PRIVATE_KEY src/{ContractFile.sol}:{ContractName} --legacy
```
which executes the following:
- Does a forge create.
- Passes the RPC_URL and PVTKEY.
- References the actual smart contract.
For example, when deploying the Sbt.sol contract, the command looks like this:
```
forge create --rpc-url $RPC_URL --private-key $PRIVATE_KEY src/Sbt.sol:SoEarly --legacy
```

The above command compiles and deploys the contract to the zkEVM Testnet. The output on the CLI looks like this one below.

Successful Deploy Sbt.sol

Check deployed contract in explorer¶

Copy the address of your newly deployed contract (i.e. the Deployed to: address as in the above example output).
Go to the zkEVM Testnet Explorer, and paste the address in the Search by address field.
Check Transaction Details reflecting the From address, which is the owner’s address and the To address, which is the same Deployed to: address seen in the CLI.