How to Create and Deploy an XRC721 NFT Using Truffle

Use Truffle to deploy an XRC721 Token.

🧭 Table of contents

📰 Overview

Truffle is a blockchain development environment, which you can use to create and test smart contracts by leveraging an Ethereum Virtual Machine.

What you will learn

In this tutorial, you will learn how to set up Truffle and use it to build, test, and deploy a XRC721 Token on both the XDC Network mainnet and XDC Apothem testnet.

What you will do

  • Install and setup Truffle

  • Create an XRC721 token

  • Compile the XRC721 token

  • Deploy the XRC721 token

  • Interact with the XRC721 token

  • Check the deployment status on xinfin.network

📰 About XRC721 Tokens

XRC721 is a set of rules to standardize assets on the XDC network. Every XRC721 Token must be able to execute the following methods:

  • safeTransferFrom(address from, address to, uint256 tokenId)

  • transferFrom(address from, address to, uint256 tokenId)

  • approve(address to, uint256 tokenId)

  • getApproved(uint256 tokenId)

  • setApprovalForAll(address operator, bool _approved)

  • isApprovedForAll(address owner, address operator)

These are the minimum required methods that allow an asset on the XDC network to be called an XRC721 token. Also, a XRC721 token must be able to emit the following Events on the blockchain:

  • Approval(address indexed owner, address indexed approved, uint256 indexed tokenId)

  • Transfer(address indexed from, address indexed to, uint256 indexed tokenId)

  • ApprovalForAll(address indexed owner, address indexed operator, bool approved)

Events are helpers that come in handy in the exhaustive labor of indexing state changes, and they are essential for off-chain applications to find relevant data on the blockchain. By mapping all Transfer events, for example, we can fetch all the historic data on token transfers more easily.

Last but not least, a couple contract constants that are public that are also very important to have are:

  • name

  • symbol

Without these public constants, it would be impossible to label tokens on block explorers, for example. In this tutorial we will deploy a XRC721 token that have all the Methods, Events and Constants mentioned above.

🚀 Setting up the development environment

There are a few technical requirements before you start. Please install the following:

Once you have those installed, you only need one command to install Truffle:

npm install -g truffle

To verify that Truffle is installed properly, type truffle version in terminal. You should see something like:

Truffle v5.5.27 (core: 5.5.27)
Ganache v7.4.0
Solidity v0.5.16 (solc-js)
Node v16.16.0
Web3.js v1.7.4

If you see an error instead, make sure that your npm modules are added to your path.

⚒ Starting a new Truffle Project

Start by setting up your folder. The project will be called XRC721, and you can create a new XRC721 folder by running the following on terminal:

mkdir XRC721 && cd XRC721

Next, run truffle init. If truffle is correctly installed on your local environment, you should see the following message:

Starting init...
================

> Copying project files to /home/your/path/to/XRC721

Init successful. Sweet!

Try our scaffold commands to get started:
  $ truffle create contract YourContractName # scaffold a contract
  $ truffle create test YourTestName         # scaffold a test

http://trufflesuite.com/docs

Your folder files will look like this:

⚒ Configuring the XDC Mainnet and the Apothem Testnet on Truffle

In order to get started deploying new contracts on XDC Mainnet and/or Apothem, we need to install two new dependencies that will be used in the truffle-config.js file. These dependencies are @truffle/hdwallet-provider and dotenv. First, choose your preferred package manager. In this example, we are using yarn but you can also use npm.

If you never used yarn before, you might need to install it first. ‼️You can skip this step if you already have yarn installed‼️

npm install --global yarn

Initialize your package manager in your folder and install the required dependencies:

yarn init -y
yarn add @truffle/hdwallet-provider dotenv

You will also need a 24-Word Mnemonic Phrase. To configure your wallet, create a new .env file and write your mnemonic by running:

touch .env
echo MNEMONIC=arm derive cupboard decade course garlic journey blast tribe describe curve obey >> .env

Remember to change the 24-Word Mnemonic above for your own mnemonic. The contents of your .env file should read as follow:

MNEMONIC=arm derive cupboard decade course garlic journey blast tribe describe curve obey

🚨 Do not use the mnemonic in the example above in production or you may risk losing your assets and/or the ownership of your smart contracts! 🚨

Finally, you can configure the truffle-config.js file for both Apothem and XinFin Networks by writting:

require('dotenv').config();
const { MNEMONIC } = process.env;
const HDWalletProvider = require('@truffle/hdwallet-provider');

module.exports = {

  networks: {

    xinfin: {
      provider: () => new HDWalletProvider(
        MNEMONIC,
        'https://erpc.xinfin.network'),
      network_id: 50,
      gasLimit: 6721975,
      confirmation: 2,
    },

    apothem: {
      provider: () => new HDWalletProvider(
        MNEMONIC,
        'https://erpc.apothem.network'),
      network_id: 51,
      gasLimit: 6721975,
      confirmation: 2,
    }
  },

  mocha: {
  },

  compilers: {
    solc: {
      version: "0.8.16",
    }
  },
};

⚒ Adding Testnet XDC to Development Wallet

It is possible to list all XDC addresses bound to your mnemonic on Truffle by accessing the Truffle console:

truffle console --network xinfin

Once the Truffle console CLI opens, you can run:

truffle(xinfin)> accounts

And the console should log all accounts bound to your mnemonic phrase as follow:

[
  '0xA4e66f4Cc17752f331eaC6A20C00756156719519',
  '0x0431d52FE37F3839895018272dfa3bA189fcE07E',
  '0x11A6D9727c16064950473a4c8A92dC294190f7fF',
  '0x4464DDF9969E9a8e5CfF02E3706AEB4ccA92A314',
  '0xFa73bE6AA126DEC47ce14a22B7BAaF8BAFaB59Fb',
  '0xEdFFc4e7476f05f43cA3e6f5784349dE6E6373D5',
  '0x07795c732Bb013165FADCE64B884bf9971Bf9636',
  '0x5dF551A53bEaAB8bb2307eF459aA5AAFbb5F73cc',
  '0x910435b01e6Aa66dE22769062998F6AE98566f23',
  '0x573b009b2dE9A95531f82DA10BB0D793050329d2'
]

These accounts are on the Ethereum standard format starting with 0x, but we can simply switch 0x for xdc. By default, the deployment account is the first account from the list above: xdcA4e66f4Cc17752f331eaC6A20C00756156719519.

With this account in hand, you can head to the Apothem Faucet and claim some TXDC for development purposes:

💵 Writing our first XRC721 Token

The source code for the XRC721 Token used in this tutorial is available here: XRC721 Contract Folder. But we have addressed all Events, Methods and Constants mentioned in the section 📰 About XRC721 Tokens.

You can start by creating the XRC721.sol file:

touch ./contracts/XRC721.sol

Write the shell of our smart contract by writing:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract XRC721 {
    
}

💵 OpenZeppelin

Inside our contract, we will be importing the scripts from OpenZeppelin Github repository. These form the foundation for our contract which is having all the code of different functions which needs to be implemented in our contract. We are also importing the Counters from OpenZeppelin Github repository which is used to keep account of the counter of the current tokenId.

First, you must import OpenZeppelin using this command:

npm i @openzeppelin/contracts

Next, you have to import both ERC721 and Counters contract to our code:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.16;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/utils/Counters.sol";

contract XRC721 is ERC721 {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;
    
}

💵 Events and Functions

As mentioned in 📰 About XRC721 Tokens, events are very important part of a smart contract logic. Events have indexed variables that can be filtered by off-chain interfaces. We might be tempted to index all the variables that are tied to an on-chain event, however Solidity has a maximum of 3 indexed variable limitation for Events. This is how Transfer, Approval and ApprovalForAll are written in OpenZeppelin in a simpler form:

contract IXRC721 {
  event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
  
  event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
  
  event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
  
  // Mapping from token ID to owner
  mapping(uint256 => address) private _tokenOwner;

  // Mapping from owner to number of owned token
  mapping(address => Counters.Counter) private _ownedTokensCount;
  
  // Mapping from token ID to approved address
  mapping(uint256 => address) private _tokenApprovals;
  
  // Mapping from owner to operator approvals
  mapping(address => mapping(address => bool)) private _operatorApprovals;
  
  /* @dev Returns the number of NFTs in `owner`'s account. */
  function balanceOf(address owner) public view returns (uint256) {
      require(owner != address(0), "XRC721: balance query for the zero address");
      return _ownedTokensCount[owner].current();
  }
  
  /* @dev Returns the owner of the NFT specified by `tokenId`.*/
  function ownerOf(uint256 tokenId) public view virtual returns (address) {
      address owner = _owners[tokenId];
      require(owner != address(0), "ERC721: owner query for nonexistent token");
      return owner;
  }
  
  * - If the caller is not `from`, it must be have been allowed to move this
  * NFT by either {approve} or {setApprovalForAll}.
  */
  function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public {
      require(_isApprovedOrOwner(_msgSender(), tokenId), "XRC721: transfer caller is not owner nor approved");
      _safeTransferFrom(from, to, tokenId, _data);
  }
  
  function transferFrom(address from, address to, uint256 tokenId) public {
      //solhint-disable-next-line max-line-length
      require(_isApprovedOrOwner(_msgSender(), tokenId), "XRC721: transfer caller is not owner nor approved");
      _transferFrom(from, to, tokenId);
  }
  
  function _approve(address to, uint256 tokenId) internal virtual {
      _tokenApprovals[tokenId] = to;
      emit Approval(ownerOf(tokenId), to, tokenId);
  }
  
  function getApproved(uint256 tokenId) public view returns (address operator) {
      require(_exists(tokenId), "ERC721: approved query for nonexistent token");

      return _tokenApprovals[tokenId];
  }
  
  function setApprovalForAll(address to, bool approved) public {
      require(to != _msgSender(), "XRC721: approve to caller");
      _operatorApprovals[_msgSender()][to] = approved;
      emit ApprovalForAll(_msgSender(), to, approved);
  }
  
  function isApprovedForAll(address owner, address operator) public view virtual returns (bool) {
      return _operatorApprovals[owner][operator];
  }
}

You don't need to write this code in tour contract. It is already implemented with the OpenZeppelin github repository.

💵 Methods

Next, you will create the constructor. This function is called only once, when the contract is deployed, and you can attach information such as the token name and symbol. You can also create another function createToken which will take an address and mint our created XRC721 NFT Token to that address:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.16;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/utils/Counters.sol";

contract XRC721 is ERC721 {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    constructor(string memory _name, string memory _symbol) ERC721(_name, _symbol) {
    }

    function createToken(address tokenOwner) public returns (uint256) {
        _tokenIds.increment();
        uint256 newItemId = _tokenIds.current();
        _mint(tokenOwner, newItemId);
        return newItemId;
    }
}

Now you have implemented everything you need to make your token compliant with the XRC721 standard. Of course, there are more features we can implement to this contract, such as the SafeMath library that replaces naive mathematical operations for methods that will avoid underflows and overflows, and supply management methods such as mint and burn.

💵 Compiling and Deploying

We can compile our XRC721.sol by running:

truffle compile

If everything is correctly configured and there is no errors, you should see the following message on your console:

Compiling your contracts...
===========================
> Compiling @openzeppelin\contracts\token\ERC721\ERC721.sol
> Compiling @openzeppelin\contracts\token\ERC721\IERC721.sol
> Compiling @openzeppelin\contracts\token\ERC721\IERC721Receiver.sol
> Compiling @openzeppelin\contracts\token\ERC721\extensions\IERC721Metadata.sol
> Compiling @openzeppelin\contracts\utils\Address.sol
> Compiling @openzeppelin\contracts\utils\Context.sol
> Compiling @openzeppelin\contracts\utils\Counters.sol
> Compiling @openzeppelin\contracts\utils\Strings.sol
> Compiling @openzeppelin\contracts\utils\introspection\ERC165.sol
> Compiling @openzeppelin\contracts\utils\introspection\IERC165.sol
> Compiling .\contracts\XRC721.sol
> Artifacts written to E:\XDC-Documentation\XRC721\Truffle\XRC721\build\contracts
> Compiled successfully using:
   - solc: 0.8.16+commit.07a7930e.Emscripten.clang

Your folder should look like this:

In order to deploy your newly compiled contract artifacts to the blockchain, you'll need to create a deployment script into the migrations folder:

touch ./migrations/1_token_migration.js

Write the following migration script to the 1_token_migration.js file:

const XRC721Token = artifacts.require("XRC721");

const NAME = "MyToken";
const SYMBOL = "MTK";

module.exports = function (deployer) {
    deployer.deploy(XRC721Token, NAME, SYMBOL);
}

If the migration script has no errors, we can go ahead and run the command (for the deployment on the XDC Mainnet:

truffle migrate --network xinfin

Or, for deplloyment on the XDC Apothem Testnet:

truffle migrate --network apothem

In either case, you must have enough funds to pay for gas fees on the address that is being used for development.

If the deployment is successful, the console should log the following message after migrations complete processing:

1_token_migration.js
====================

   Deploying 'XRC721Token'
   ----------------------
   > transaction hash:    0x5cc1de32af041ff64ec2a4cef503b31ac996ae56dc33338d473ba04775492136
   > Blocks: 2            Seconds: 5
   > contract address:    0x53bA8Cb12EaF09E6B0b671F39ac4798A6DA7d660
   > block number:        50472279
   > block timestamp:     1663446177
   > account:             0xA4e66f4Cc17752f331eaC6A20C00756156719519
   > balance:             24.511102145
   > gas used:            1121906 (0x111e72)
   > gas price:           0.25 gwei
   > value sent:          0 ETH
   > total cost:          0.0002804765 ETH

   > Saving artifacts
   -------------------------------------
   > Total cost:        0.0002804765 ETH

Summary
=======
> Total deployments:   1
> Final cost:          0.0002804765 ETH

🔍 Veryfing Contracts on the Block Explorer

Once you have successfully deployed your smart contract to the blockchain, it might be interesting to verify you contract on XinFin Block Explorer.

First, check the address your contract is deployed to by running:

truffle networks

If you have a contract already deployed, the console should log something like this:

Network: apothem (id: 51)
  No contracts deployed.

Network: xinfin (id: 50)
  XRC721Token: 0x53bA8Cb12EaF09E6B0b671F39ac4798A6DA7d660

In this example, you'd have a XRC721 contract deployed on XDC Mainnet at the 0x53bA8Cb12EaF09E6B0b671F39ac4798A6DA7d660. This address is in the Ethereum standard but we can simply swap the 0x prefix for xdc and search for our newly deployed contract on XinFin Block Explorer:

Next, click the Verify And Publish Option.

You'll be redirected to the contract verification page where you will need to fill out:

  • Contract Name: XRC721Token

  • Compiler: Check your truffle-config.js file for Compiler Version

  • Contract Code: Just paste everything from your MyToken.sol file

Once everything is filled out, press Submit!

If everything is correctly filled out, your contract page on the block explorer should display a new tab called Contract:

🔍 Interacting with your contract on the Block Explorer

You can check for the minted token by going to our XDCPay Wallet and clicking on the Tokens tab and click on the Add Token button.

Next, you have to add the deployed contract address on the Token Address text field. This will automatically fetch the token symbol. Click on the Add Token button.

Your newly minted token is available in your wallet.

You can also check our successful transaction on the Block Explorer!

For more information about Truffle Suite, Please Visit Truffle Suite Documentation. For more information about XinFin Network, Please Visit XDC Network Documentation on GitBook.\

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