Allow NFT minting only to whitelisted accounts by verifying merkle proof in Solidity contract. Merkle root and merkle proofs are constructed using MerkleTree.js.
pragma solidity ^0.8.0;
import "@openzeppelin/contracts/utils/cryptography/MerkleProof.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
contract WhitelistSale is ERC721 {
bytes32 immutable public merkleRoot;
uint256 public nextTokenId;
mapping(address => bool) public claimed;
constructor(bytes32 _merkleRoot) ERC721("ExampleNFT", "NFT") {
merkleRoot = _merkleRoot;
}
function toBytes32(address addr) pure internal returns (bytes32) {
return bytes32(uint256(uint160(addr)));
}
function mint(bytes32[] calldata merkleProof) public payable {
require(claimed[msg.sender] == false, "already claimed");
claimed[msg.sender] = true;
require(MerkleProof.verify(merkleProof, merkleRoot, toBytes32(msg.sender)) == true, "invalid merkle proof");
nextTokenId++;
_mint(msg.sender, nextTokenId);
}
}const { expect, use } = require('chai')
const { ethers } = require('hardhat')
const { MerkleTree } = require('merkletreejs')
const { keccak256 } = ethers.utils
use(require('chai-as-promised'))
describe('WhitelistSale', function () {
it('allow only whitelisted accounts to mint', async () => {
const accounts = await hre.ethers.getSigners()
const whitelisted = accounts.slice(0, 5)
const notWhitelisted = accounts.slice(5, 10)
const padBuffer = (addr) => {
return Buffer.from(addr.substr(2).padStart(32*2, 0), 'hex')
}
const leaves = whitelisted.map(account => padBuffer(account.address))
const tree = new MerkleTree(leaves, keccak256, { sort: true })
const merkleRoot = tree.getHexRoot()
const WhitelistSale = await ethers.getContractFactory('WhitelistSale')
const whitelistSale = await WhitelistSale.deploy(merkleRoot)
await whitelistSale.deployed()
const merkleProof = tree.getHexProof(padBuffer(whitelisted[0].address))
const invalidMerkleProof = tree.getHexProof(padBuffer(notWhitelisted[0].address))
await expect(whitelistSale.mint(merkleProof)).to.not.be.rejected
await expect(whitelistSale.mint(merkleProof)).to.be.rejectedWith('already claimed')
await expect(whitelistSale.connect(notWhitelisted[0]).mint(invalidMerkleProof)).to.be.rejectedWith('invalid merkle proof')
})
})Install dependencies
npm installRun test
npm test
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