Exercise 2: Build Your First Cross-Chain NFT

Coding Time 🎉

CCIP Config Details

Arbitrum Sepolia
Ethereum Sepolia

Chain Selector

3478487238524512106
16015286601757825753

CCIP Router Address

0x2a9c5afb0d0e4bab2bcdae109ec4b0c4be15a165

0x0bf3de8c5d3e8a2b34d2beeb17abfcebaf363a59

LINK Token Address

0xb1D4538B4571d411F07960EF2838Ce337FE1E80E

0x779877A7B0D9E8603169DdbD7836e478b4624789

Getting started

You can use Chainlink CCIP with any blockchain development framework. For this Masterclass, we prepared the steps for Hardhat, Foundry, and Remix IDE.

Let's create a new project

Make sure you have Node.js and NPM installed. To check, run the following command:

node -v
npm -v

Create a new folder and name it ccip-masterclass-3

mkdir ccip-masterclass-3

Navigate to it

cd ccip-masterclass-3

Create a hew Hardhat project by running:

npx hardhat init

And then select "Create a TypeScript project".

Alternatively, you can clone:

The @chainlink/contracts-ccip NPM package

To use Chainlink CCIP, you need to interact with Chainlink CCIP-specific contracts from the @chainlink/contracts-ccip NPM package.

https://www.npmjs.com/package/@chainlink/contracts-ccipwww.npmjs.com

To install it, follow steps specific to the development environment you will use for this Masterclass.

npm i @chainlink/contracts-ccip --save-dev

We will need a standard @chainlink/contracts NPM package for this Module as well, so let's install it too while we are here by running the following command:

npm i @chainlink/contracts --save-dev

Finally, for this exercise we will need to install and the @openzeppelin/contracts NPM package, as well. To do so, run:

npm i @openzeppelin/contracts --save-dev

Faucet

To pay for CCIP Fees you can use either LINK token or native/wrapped native asset on a given blockchain. For this exercise we will need at least 1 LINK or Arbitrum Sepolia testnet. To get it, navigate to the https://faucets.chain.link/arbitrum-sepolia

LogoArbitrum Sepolia Faucet - Get Testnet Tokensfaucets.chain.link
Chainlink Faucets

Develop xNFT smart contract

Create a new file inside the contracts folder and name it XNFT.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import {ERC721URIStorage} from "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import {ERC721Burnable} from "@openzeppelin/contracts/token/ERC721/extensions/ERC721Burnable.sol";
import {IERC20} from "@openzeppelin/contracts/interfaces/IERC20.sol";
import {SafeERC20} from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import {ReentrancyGuard} from "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import {Client} from "@chainlink/contracts-ccip/src/v0.8/ccip/libraries/Client.sol";
import {IRouterClient} from "@chainlink/contracts-ccip/src/v0.8/ccip/interfaces/IRouterClient.sol";
import {IAny2EVMMessageReceiver} from "@chainlink/contracts-ccip/src/v0.8/ccip/interfaces/IAny2EVMMessageReceiver.sol";
import {OwnerIsCreator} from "@chainlink/contracts-ccip/src/v0.8/shared/access/OwnerIsCreator.sol";
import {LinkTokenInterface} from "@chainlink/contracts/src/v0.8/interfaces/LinkTokenInterface.sol";

/**
 * THIS IS AN EXAMPLE CONTRACT THAT USES HARDCODED VALUES FOR CLARITY.
 * THIS IS AN EXAMPLE CONTRACT THAT USES UN-AUDITED CODE.
 * DO NOT USE THIS CODE IN PRODUCTION.
 */
contract XNFT is
    ERC721,
    ERC721URIStorage,
    ERC721Burnable,
    IAny2EVMMessageReceiver,
    ReentrancyGuard,
    OwnerIsCreator
{
    using SafeERC20 for IERC20;

    enum PayFeesIn {
        Native,
        LINK
    }

    error InvalidRouter(address router);
    error OnlyOnArbitrumSepolia();
    error NotEnoughBalanceForFees(
        uint256 currentBalance,
        uint256 calculatedFees
    );
    error NothingToWithdraw();
    error FailedToWithdrawEth(address owner, address target, uint256 value);
    error ChainNotEnabled(uint64 chainSelector);
    error SenderNotEnabled(address sender);
    error OperationNotAllowedOnCurrentChain(uint64 chainSelector);

    struct XNftDetails {
        address xNftAddress;
        bytes ccipExtraArgsBytes;
    }

    uint256 constant ARBITRUM_SEPOLIA_CHAIN_ID = 421614;

    string[] characters = [
        "https://ipfs.io/ipfs/QmTgqnhFBMkfT9s8PHKcdXBn1f5bG3Q5hmBaR4U6hoTvb1?filename=Chainlink_Elf.png",
        "https://ipfs.io/ipfs/QmZGQA92ri1jfzSu61JRaNQXYg1bLuM7p8YT83DzFA2KLH?filename=Chainlink_Knight.png",
        "https://ipfs.io/ipfs/QmW1toapYs7M29rzLXTENn3pbvwe8ioikX1PwzACzjfdHP?filename=Chainlink_Orc.png",
        "https://ipfs.io/ipfs/QmPMwQtFpEdKrUjpQJfoTeZS1aVSeuJT6Mof7uV29AcUpF?filename=Chainlink_Witch.png"
    ];

    IRouterClient internal immutable i_ccipRouter;
    LinkTokenInterface internal immutable i_linkToken;
    uint64 private immutable i_currentChainSelector;

    uint256 private _nextTokenId;

    mapping(uint64 destChainSelector => XNftDetails xNftDetailsPerChain)
        public s_chains;

    event ChainEnabled(
        uint64 chainSelector,
        address xNftAddress,
        bytes ccipExtraArgs
    );
    event ChainDisabled(uint64 chainSelector);
    event CrossChainSent(
        address from,
        address to,
        uint256 tokenId,
        uint64 sourceChainSelector,
        uint64 destinationChainSelector
    );
    event CrossChainReceived(
        address from,
        address to,
        uint256 tokenId,
        uint64 sourceChainSelector,
        uint64 destinationChainSelector
    );

    modifier onlyRouter() {
        if (msg.sender != address(i_ccipRouter))
            revert InvalidRouter(msg.sender);
        _;
    }

    modifier onlyOnArbitrumSepolia() {
        if (block.chainid != ARBITRUM_SEPOLIA_CHAIN_ID)
            revert OnlyOnArbitrumSepolia();
        _;
    }

    modifier onlyEnabledChain(uint64 _chainSelector) {
        if (s_chains[_chainSelector].xNftAddress == address(0))
            revert ChainNotEnabled(_chainSelector);
        _;
    }

    modifier onlyEnabledSender(uint64 _chainSelector, address _sender) {
        if (s_chains[_chainSelector].xNftAddress != _sender)
            revert SenderNotEnabled(_sender);
        _;
    }

    modifier onlyOtherChains(uint64 _chainSelector) {
        if (_chainSelector == i_currentChainSelector)
            revert OperationNotAllowedOnCurrentChain(_chainSelector);
        _;
    }

    constructor(
        address ccipRouterAddress,
        address linkTokenAddress,
        uint64 currentChainSelector
    ) ERC721("Cross Chain NFT", "XNFT") {
        if (ccipRouterAddress == address(0)) revert InvalidRouter(address(0));
        i_ccipRouter = IRouterClient(ccipRouterAddress);
        i_linkToken = LinkTokenInterface(linkTokenAddress);
        i_currentChainSelector = currentChainSelector;
    }

    function mint() external onlyOnArbitrumSepolia {
        uint256 tokenId = _nextTokenId++;
        string memory uri = characters[tokenId % characters.length];
        _safeMint(msg.sender, tokenId);
        _setTokenURI(tokenId, uri);
    }

    function enableChain(
        uint64 chainSelector,
        address xNftAddress,
        bytes memory ccipExtraArgs
    ) external onlyOwner onlyOtherChains(chainSelector) {
        s_chains[chainSelector] = XNftDetails({
            xNftAddress: xNftAddress,
            ccipExtraArgsBytes: ccipExtraArgs
        });

        emit ChainEnabled(chainSelector, xNftAddress, ccipExtraArgs);
    }

    function disableChain(
        uint64 chainSelector
    ) external onlyOwner onlyOtherChains(chainSelector) {
        delete s_chains[chainSelector];

        emit ChainDisabled(chainSelector);
    }

    function crossChainTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        uint64 destinationChainSelector,
        PayFeesIn payFeesIn
    )
        external
        nonReentrant
        onlyEnabledChain(destinationChainSelector)
        returns (bytes32 messageId)
    {
        string memory tokenUri = tokenURI(tokenId);
        _burn(tokenId);

        Client.EVM2AnyMessage memory message = Client.EVM2AnyMessage({
            receiver: abi.encode(
                s_chains[destinationChainSelector].xNftAddress
            ),
            data: abi.encode(from, to, tokenId, tokenUri),
            tokenAmounts: new Client.EVMTokenAmount[](0),
            extraArgs: s_chains[destinationChainSelector].ccipExtraArgsBytes,
            feeToken: payFeesIn == PayFeesIn.LINK
                ? address(i_linkToken)
                : address(0)
        });

        // Get the fee required to send the CCIP message
        uint256 fees = i_ccipRouter.getFee(destinationChainSelector, message);

        if (payFeesIn == PayFeesIn.LINK) {
            if (fees > i_linkToken.balanceOf(address(this)))
                revert NotEnoughBalanceForFees(
                    i_linkToken.balanceOf(address(this)),
                    fees
                );

            // Approve the Router to transfer LINK tokens on contract's behalf. It will spend the fees in LINK
            i_linkToken.approve(address(i_ccipRouter), fees);

            // Send the message through the router and store the returned message ID
            messageId = i_ccipRouter.ccipSend(
                destinationChainSelector,
                message
            );
        } else {
            if (fees > address(this).balance)
                revert NotEnoughBalanceForFees(address(this).balance, fees);

            // Send the message through the router and store the returned message ID
            messageId = i_ccipRouter.ccipSend{value: fees}(
                destinationChainSelector,
                message
            );
        }

        emit CrossChainSent(
            from,
            to,
            tokenId,
            i_currentChainSelector,
            destinationChainSelector
        );
    }

    /// @inheritdoc IAny2EVMMessageReceiver
    function ccipReceive(
        Client.Any2EVMMessage calldata message
    )
        external
        virtual
        override
        onlyRouter
        nonReentrant
        onlyEnabledChain(message.sourceChainSelector)
        onlyEnabledSender(
            message.sourceChainSelector,
            abi.decode(message.sender, (address))
        )
    {
        uint64 sourceChainSelector = message.sourceChainSelector;
        (
            address from,
            address to,
            uint256 tokenId,
            string memory tokenUri
        ) = abi.decode(message.data, (address, address, uint256, string));

        _safeMint(to, tokenId);
        _setTokenURI(tokenId, tokenUri);

        emit CrossChainReceived(
            from,
            to,
            tokenId,
            sourceChainSelector,
            i_currentChainSelector
        );
    }

    function withdraw(address _beneficiary) public onlyOwner {
        uint256 amount = address(this).balance;

        if (amount == 0) revert NothingToWithdraw();

        (bool sent, ) = _beneficiary.call{value: amount}("");

        if (!sent) revert FailedToWithdrawEth(msg.sender, _beneficiary, amount);
    }

    function withdrawToken(
        address _beneficiary,
        address _token
    ) public onlyOwner {
        uint256 amount = IERC20(_token).balanceOf(address(this));

        if (amount == 0) revert NothingToWithdraw();

        IERC20(_token).safeTransfer(_beneficiary, amount);
    }

    function tokenURI(
        uint256 tokenId
    ) public view override(ERC721, ERC721URIStorage) returns (string memory) {
        return super.tokenURI(tokenId);
    }

    function getCCIPRouter() public view returns (address) {
        return address(i_ccipRouter);
    }

    function supportsInterface(
        bytes4 interfaceId
    ) public view override(ERC721, ERC721URIStorage) returns (bool) {
        return
            interfaceId == type(IAny2EVMMessageReceiver).interfaceId ||
            super.supportsInterface(interfaceId);
    }
}

Compile your contract by running:

npx hardhat compile

Prepare for deployment

Follow the steps to add the necessary environment variables for deploying these contracts and sending your first CCIP Message.

This contract expects at least 0.8.20 Solidity version. It is very important to understand that with Solc version 0.8.20, the default EVM version is set to "Shanghai". A new opcode, PUSH0, was added to the Ethereum Virtual Machine in the Shanghai upgrade.

However, besides Ethereum, the majority of blockchains haven't included PUSH0 opcode.

That means the PUSH0 opcode can now be part of the contract's bytecode and if the chain you are working on does not support it, it will error with the "Invalid opcode" error.

To understand more, we highly encourage you to check this StackOverflow answer:

LogoRemix: Returned error: {"jsonrpc":"2.0","error":"invalid opcode: PUSH0", "id":2405507186007008}Stack Overflow
Setting solc EVM version in different environments

We are going to use the @chainlink/env-enc package for extra security. It encrypts sensitive data instead of storing them as plain text in the .env file by creating a new .env.enc file. Although it's not recommended to push this file online, if that accidentally happens, your secrets will still be encrypted.

Install the package by running the following command:

npm i @chainlink/env-enc --save-dev

Set a password for encrypting and decrypting the environment variable file. You can change it later by typing the same command.

npx env-enc set-pw

Now set the following environment variables: PRIVATE_KEY, Source Blockchain RPC URL, Destination Blockchain RPC URL. For this example, we are going to use Arbitrum Sepolia and Ethereum Sepolia.

PRIVATE_KEY=""
ARBITRUM_SEPOLIA_RPC_URL=""
ETHEREUM_SEPOLIA_RPC_URL=""

To set these variables, type the following command and follow the instructions in the terminal:

npx env-enc set

After you are done, the .env.enc file will be automatically generated. If you want to validate your inputs, you can always run the next command:

npx env-enc view

Finally, expand the hardhat.config to support these two networks:

import * as dotenvenc from '@chainlink/env-enc'
dotenvenc.config();

import { HardhatUserConfig } from 'hardhat/config';
import '@nomicfoundation/hardhat-toolbox';

const PRIVATE_KEY = process.env.PRIVATE_KEY;
const ARBITRUM_SEPOLIA_RPC_URL = process.env.ARBITRUM_SEPOLIA_RPC_URL;
const ETHEREUM_SEPOLIA_RPC_URL = process.env.ETHEREUM_SEPOLIA_RPC_URL;

const config: HardhatUserConfig = {
  solidity: {
    compilers: [
      {
          version: '0.8.20',
          settings: {
              evmVersion: 'paris'
          }
      }
    ]
  },
  networks: {
    hardhat: {
      chainId: 31337
    },
    arbitrumSepolia: {
      url: ARBITRUM_SEPOLIA_RPC_URL !== undefined ? ARBITRUM_SEPOLIA_RPC_URL : '',
      accounts: PRIVATE_KEY !== undefined ? [PRIVATE_KEY] : [],
      chainId: 421614
    },
    ethereumSepolia: {
      url: ETHEREUM_SEPOLIA_RPC_URL !== undefined ? ETHEREUM_SEPOLIA_RPC_URL : '',
      accounts: PRIVATE_KEY !== undefined ? [PRIVATE_KEY] : [],
      chainId: 11155111
    },
  }
};

export default config;

Step 1) Deploy XNFT.sol to Ethereum Sepolia

Prepare Chain Selector and CCIP Router & LINK token addresses on Ethereum Sepolia. You can get them if you scroll to the beginning of this page, at CCIP Config Details

Navigate to the scripts folder and create new file named deployXNFT.ts

// deployXNFT.ts

import { ethers, network } from "hardhat";

async function main() {
    const ccipRouterAddressEthereumSepolia = `0x0bf3de8c5d3e8a2b34d2beeb17abfcebaf363a59`;
    const linkTokenAddressEthereumSepolia = `0x779877A7B0D9E8603169DdbD7836e478b4624789`;
    const chainIdEthereumSepolia = `16015286601757825753`;

    const xNft = await ethers.deployContract("XNFT", [
        ccipRouterAddressEthereumSepolia,
        linkTokenAddressEthereumSepolia,
        chainIdEthereumSepolia
    ]);

    await xNft.waitForDeployment();

    console.log(`XNFT deployed on ${network.name} with address ${xNft.target}`);
}

// We recommend this pattern to be able to use async/await everywhere
// and properly handle errors.
main().catch((error) => {
    console.error(error);
    process.exitCode = 1;
});

Run the deployment script:

npx hardhat run ./scripts/deployXNFT.ts --network ethereumSepolia

Step 2) Deploy XNFT.sol to Arbitrum Sepolia

Prepare Chain Selector and CCIP Router & LINK token addresses on Arbitrum Sepolia. You can get them if you scroll to beginning of this page, at CCIP Config Details

Navigate to the scripts folder and create new file named deployXNFTArbitrum.ts

// deployXNFTArbitrum.ts

import { ethers, network } from "hardhat";

async function main() {
    const ccipRouterAddressArbitrumSepolia = `0x2a9c5afb0d0e4bab2bcdae109ec4b0c4be15a165`;
    const linkTokenAddressArbitrumSepolia = `0xb1D4538B4571d411F07960EF2838Ce337FE1E80E`;
    const chainIdArbitrumSepolia = `3478487238524512106`;

    const xNft = await ethers.deployContract("XNFT", [
        ccipRouterAddressArbitrumSepolia,
        linkTokenAddressArbitrumSepolia,
        chainIdArbitrumSepolia
    ]);

    await xNft.waitForDeployment();

    console.log(`XNFT deployed on ${network.name} with address ${xNft.target}`);
}

// We recommend this pattern to be able to use async/await everywhere
// and properly handle errors.
main().catch((error) => {
    console.error(error);
    process.exitCode = 1;
});

Run the deployment script:

npx hardhat run ./scripts/deployXNFTArbitrum.ts --network arbitrumSepolia

Step 3) On Ethereum Sepolia, call enableChain function

Prepare:

  • The address of the address of the XNFT.sol smart contract you previously deployed to Ethereum Sepolia;

  • The address of the address of the XNFT.sol smart contract you previously deployed to Arbitrum Sepolia;

  • 3478487238524512106, which is the CCIP Chain Selector for the Arbitrum Sepolia network, as the chainSelector parameter;

  • 0x97a657c90000000000000000000000000000000000000000000000000000000000030d40, which is the bytes version of CCIP extraArgs' default value with 200_000 gas set for gasLimit, as ccipExtraArgs parameter.

If you would like to calculate this value by yourself, you can reuse the following helper smart contract:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import {Client} from "@chainlink/contracts-ccip/src/v0.8/ccip/libraries/Client.sol";

contract EncodeExtraArgs {
  // Below is a simplistic example (same params for all messages) of using storage to allow for new options without
  // upgrading the dapp. Note that extra args are chain family specific (e.g. gasLimit is EVM specific etc.).
  // and will always be backwards compatible i.e. upgrades are opt-in.
  // Offchain we can compute the V1 extraArgs:
  //    Client.EVMExtraArgsV1 memory extraArgs = Client.EVMExtraArgsV1({gasLimit: 300_000});
  //    bytes memory encodedV1ExtraArgs = Client._argsToBytes(extraArgs);
  // Then later compute V2 extraArgs, for example if a refund feature was added:
  //    Client.EVMExtraArgsV2 memory extraArgs = Client.EVMExtraArgsV2({gasLimit: 300_000, destRefundAddress: 0x1234});
  //    bytes memory encodedV2ExtraArgs = Client._argsToBytes(extraArgs);
  // and update storage with the new args.
  // If different options are required for different messages, for example different gas limits,
  // one can simply key based on (chainSelector, messageType) instead of only chainSelector.

  function encode(uint256 gasLimit) external pure returns(bytes memory extraArgsBytes) {
      Client.EVMExtraArgsV1 memory extraArgs = Client.EVMExtraArgsV1({gasLimit: gasLimit});
      extraArgsBytes = Client._argsToBytes(extraArgs);
  }
}

Create a new TypeScript file under the scripts folder and name it enableChain.ts

// scripts/enableChain.ts

import { ethers, network } from "hardhat";
import { Wallet } from "ethers";
import { XNFT, XNFT__factory } from "../typechain-types";

async function main() {
  if (network.name !== `ethereumSepolia`) {
    console.error(`Must be called from Ethereum Sepolia`);
    return 1;
  }

  const privateKey = process.env.PRIVATE_KEY!;
  const rpcProviderUrl = process.env.AVALANCHE_FUJI_RPC_URL;

  const provider = new ethers.JsonRpcProvider(rpcProviderUrl);
  const wallet = new Wallet(privateKey);
  const signer = wallet.connect(provider);

  const xNftAddressEthereumSepolia = `PUT XNFT ADDRESS ON ETHEREUM SEPOLIA HERE`;
  const xNftAddressArbitrumSepolia = `PUT XNFT ADDRESS ON ARBITRUM SEPOLIA HERE`;
  const chainSelectorArbitrumSepolia = `3478487238524512106`;
  const ccipExtraArgs = `0x97a657c90000000000000000000000000000000000000000000000000000000000030d40`;

  const xNft: XNFT = XNFT__factory.connect(xNftAddressEthereumSepolia, signer);

  const tx = await xNft.enableChain(
      chainSelectorArbitrumSepolia,
      xNftAddressArbitrumSepolia,
      ccipExtraArgs
  );

  console.log(`Transaction hash: ${tx.hash}`);
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

Call the function by running the following command:

npx hardhat run ./scripts/enableChain.ts --network ethereumSepolia

Step 4) On Arbitrum Sepolia, call enableChain function

Prepare:

  • The address of the XNFT.sol smart contract you previously deployed to Arbitrum Sepolia;

  • The address of the address of the XNFT.sol smart contract you previously deployed to Ethereum Sepolia, as xNftAddress parameter;

  • 16015286601757825753, which is the CCIP Chain Selector for the Ethereum Sepolia network, as the chainSelector parameter;

  • 0x97a657c90000000000000000000000000000000000000000000000000000000000030d40, which is the bytes version of CCIP extraArgs' default value with 200_000 gas set for gasLimit, as ccipExtraArgs parameter.

If you would like to calculate this value by yourself, you can reuse the following helper smart contract:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import {Client} from "@chainlink/contracts-ccip/src/v0.8/ccip/libraries/Client.sol";

contract EncodeExtraArgs {
  // Below is a simplistic example (same params for all messages) of using storage to allow for new options without
  // upgrading the dapp. Note that extra args are chain family specific (e.g. gasLimit is EVM specific etc.).
  // and will always be backwards compatible i.e. upgrades are opt-in.
  // Offchain we can compute the V1 extraArgs:
  //    Client.EVMExtraArgsV1 memory extraArgs = Client.EVMExtraArgsV1({gasLimit: 300_000});
  //    bytes memory encodedV1ExtraArgs = Client._argsToBytes(extraArgs);
  // Then later compute V2 extraArgs, for example if a refund feature was added:
  //    Client.EVMExtraArgsV2 memory extraArgs = Client.EVMExtraArgsV2({gasLimit: 300_000, destRefundAddress: 0x1234});
  //    bytes memory encodedV2ExtraArgs = Client._argsToBytes(extraArgs);
  // and update storage with the new args.
  // If different options are required for different messages, for example different gas limits,
  // one can simply key based on (chainSelector, messageType) instead of only chainSelector.

  function encode(uint256 gasLimit) external pure returns(bytes memory extraArgsBytes) {
      Client.EVMExtraArgsV1 memory extraArgs = Client.EVMExtraArgsV1({gasLimit: gasLimit});
      extraArgsBytes = Client._argsToBytes(extraArgs);
  }
}

Create a new TypeScript file under the scripts folder and name it enableChainArbitrum.ts

// scripts/enableChainArbitrum.ts

import { ethers, network } from "hardhat";
import { Wallet } from "ethers";
import { XNFT, XNFT__factory } from "../typechain-types";

async function main() {
  if (network.name !== `arbitrumSepolia`) {
    console.error(`Must be called from Arbitrum Sepolia`);
    return 1;
  }

  const privateKey = process.env.PRIVATE_KEY!;
  const rpcProviderUrl = process.env.AVALANCHE_FUJI_RPC_URL;

  const provider = new ethers.JsonRpcProvider(rpcProviderUrl);
  const wallet = new Wallet(privateKey);
  const signer = wallet.connect(provider);

  const xNftAddressArbitrumSepolia = `PUT XNFT ADDRESS ON ARBITRUM SEPOLIA HERE`;
  const xNftAddressEthereumSepolia = `PUT XNFT ADDRESS ON ETHEREUM SEPOLIA HERE`;
  const chainSelectorEthereumSepolia = `16015286601757825753`;
  const ccipExtraArgs = `0x97a657c90000000000000000000000000000000000000000000000000000000000030d40`;

  const xNft: XNFT = XNFT__factory.connect(xNftAddressArbitrumSepolia, signer);

  const tx = await xNft.enableChain(
      chainSelectorEthereumSepolia,
      xNftAddressEthereumSepolia,
      ccipExtraArgs
  );

  console.log(`Transaction hash: ${tx.hash}`);
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

Call the function by running the following command:

npx hardhat run ./scripts/enableChainArbitrum.ts --network arbitrumSepolia

Step 5) On Arbitrum Sepolia, fund XNFT.sol with 3 LINK

To cover for CCIP fees, fund XNFT.sol with some amount of LINK, 3 should be more than enough for this demo. Obviously, for the sake of full functionality, you should fund XNFT.sol smart contract on other blockchains as well, so you can perform cross-chain transfers between all of them.

Fund your xNFT with LINK

Step 6) On Arbitrum Sepolia, mint new xNFT

Create a new TypeScript file under the scripts folder and name it mint.ts

// scripts/mint.ts

import { ethers, network } from "hardhat";
import { Wallet } from "ethers";
import { XNFT, XNFT__factory } from "../typechain-types";

async function main() {
  if (network.name !== `arbitrumSepolia`) {
    console.error(`Must be called from Arbitrum Sepolia`);
    return 1;
  }

  const privateKey = process.env.PRIVATE_KEY!;
  const rpcProviderUrl = process.env.AVALANCHE_FUJI_RPC_URL;

  const provider = new ethers.JsonRpcProvider(rpcProviderUrl);
  const wallet = new Wallet(privateKey);
  const signer = wallet.connect(provider);

  const xNftAddressArbitrumSepolia = `PUT XNFT ADDRESS ON ARBITRUM SEPOLIA HERE`;

  const xNft: XNFT = XNFT__factory.connect(xNftAddressArbitrumSepolia, signer);

  const tx = await xNft.mint();

  console.log(`Transaction hash: ${tx.hash}`);
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

Call the function by running the following command:

npx hardhat run ./scripts/mint.ts --network arbitrumSepolia

Step 7) On Arbitrum Sepolia, crossTransferFrom xNFT

Prepare:

  • Your EOA address, as the from parameter;

  • The address of an EOA on other chain where you want to cross-transfer your NFT, can be your EOA address, as to parameter;

  • The ID of a xNFT you want to cross-transfer, as tokenId parameter;

  • 16015286601757825753 which is the CCIP Chain Selector of Ethereum Sepolia blockchain, as the destinationChainSelector parameter;

  • 1 which stands that we are paying for CCIP fees in LINK, as the payFeesIn parameter.

Create a new TypeScript file under the scripts folder and name it crossChainTransferFrom.ts

// scripts/crossChainTransfer.ts

import { ethers, network } from "hardhat";
import { Wallet } from "ethers";
import { XNFT, XNFT__factory } from "../typechain-types";

async function main() {
  if (network.name !== `arbitrumSepolia`) {
    console.error(`Must be called from Arbitrum Sepolia`);
    return 1;
  }

  const privateKey = process.env.PRIVATE_KEY!;
  const rpcProviderUrl = process.env.AVALANCHE_FUJI_RPC_URL;

  const provider = new ethers.JsonRpcProvider(rpcProviderUrl);
  const wallet = new Wallet(privateKey);
  const signer = wallet.connect(provider);

  const xNftAddressArbitrumSepolia = `PUT XNFT ADDRESS ON ARBITRUM SEPOLIA HERE`;
  
  const from = `PUT YOUR EOA ADDRESS HERE`;
  const to = `PUT RECEIVER's ADDRESS HERE`;
  const tokenId = 0; // put NFT token id here
  const destinationChainSelector = `16015286601757825753`;
  const payFeesIn = 1; // 0 - Native, 1 - LINK

  const xNft: XNFT = XNFT__factory.connect(xNftAddressArbitrumSepolia, signer);

  const tx = await xNft.crossChainTransferFrom(
      from,
      to,
      tokenId,
      destinationChainSelector,
      payFeesIn
  );

  console.log(`Transaction hash: ${tx.hash}`);
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

Call the function by running the following command:

npx hardhat run ./scripts/crossChainTransfer.ts --network arbitrumSepolia

You can now monitor this cross-chain transfer on CCIP Explorer page.

CCIP Explorer

Once cross-chain NFT arrives to Ethereum Sepolia, you can manually display it inside your Metamask wallet. Navigate to the "NFT" tab and hit the "Import NFT" button.

Import NFT

Then, fill in XNFT.sol smart contract address on Ethereum Sepolia and token ID you received (0).

Fill in NFT details

Finally, your NFT will appear inside Metamask wallet.

See your newly minted NFT
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