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:
Now, test the build with forge test
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 SymbolSOE
. -
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 referencingopenzeppelin-contracts
toopenzeppelin
, which is the name used when importing. That is, changeopenzeppelin-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 calltokenuri.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 thesafeMint
function -
Remove the
uri
parameter so as to hardcode it. This results in all minted tokens sharing the same uri image, but each token’stokenId
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 thesrc
folder -
Populate
.env.sample
file with yourACCOUNT_PRIVATE_KEY
and the zkEVM Testnet’sRPC 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
andPVTKEY
. - 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
- Does a
The above command compiles and deploys the contract to the zkEVM Testnet. The output on the CLI looks like this one below.
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 theFrom
address, which is the owner’s address and theTo
address, which is the sameDeployed to:
address seen in the CLI.