Using NFT.storage

This tutorial will teach you how to use NFT.Storage to store NFTs on IPFS and Filecoin for the Harmony blockchain.

NFT.Storage is a long-term storage service designed for off-chain NFT data (like metadata, images, and other assets). Data is content addressed using IPFS, meaning the URL pointing to a piece of data (“ipfs://…”) is completely unique to that data. IPFS URLs can be used in NFTs and metadata to ensure the NFT forever actually refers to the intended data (eliminating things like rug pulls). IPFS URLs are storage layer agnostic - meaning you can store your data on many storage layers at once (whether it be on local storage, cloud storage, or multiple decentralized storage networks.

NFT.Storage stores many copies of uploaded data on the public IPFS network and Filecoin network in two primary ways: in dedicated IPFS servers managed by NFT.Storage, and decentralized on Filecoin. Since IPFS is a standard used by many different storage services, it's easy to redundantly store data uploaded to NFT.Storage on any other IPFS-compatible storage solutions.

This tutorial will walk you through the process of creating a simple NFT on Harmony, using NFT.Storage to store off-chain NFT data on IPFS and Filecoin to achieve a fully decentralized, verifiable NFT.

Overview

Write an NFT smart contract using Truffle
Connect to Harmony blockchain via Metamask
Upload your NFT assets via NFT.Storage
Invoking NFT smart contract to mint NFT via MetaMask

Prerequisites

This tutorial requires basic knowledge about Harmony blockchain, HRC721/ERC721, Truffle and Metamask.

Before you start this tutorial, make sure you have installed these necessary tools:

Part 1: Write the NFT smart contract

In this step, we will create a React application and use the Truffle framework to developer, compile, and deploy our NFT smart contract.

Create the React project and initialize Truffle
```
npx create-react-app harmony-nft
cd harmony-nft
truffle init
```
Once the project is created and initialized successfully, you will have a basic React project structure and Truffle project structure which will include:
- contracts for our smart contracts
- migrations for the deployment scripts
- truffle.js for all Truffle-related configurations

Create the Solidity contract

Next, let's create the smart contract. We will use the ERC721URIStorage contract from the Openzepplin contracts library so that our NFT contract inherits standard ERC721 functions as well as storage based token URI management.

First, install openzepplin via npm:

// run this command under harmony-nft folder
npm install @openzeppelin/contracts

Then create a HarmonyNFT.sol file under the contracts folder, and copy the ERC721URIStorage smart contract code into that file.

// SPDX-License-Identifier: UNLICENSED
pragma solidity >=0.4.22 <0.9.0;

import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/utils/Counters.sol";

contract HarmonyNFT is ERC721URIStorage{
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    event NewHarmonyNFT(address sender, uint256 tokenId, string tokenURI);
    
    //Deploy EPC721 with name and description specified.
    constructor() ERC721 ("ETH on Harmony using NFT.Storage", "HNFT") {}

	//Mint a new NFT Item and update its tokenURI with IPFS link.
    function mintItem(string memory tokenURI) public{
        _tokenIds.increment();
        uint256 newItemId = _tokenIds.current();
        _mint(msg.sender, newItemId);
        _setTokenURI(newItemId, tokenURI);
        emit NewHarmonyNFT(msg.sender, newItemId, tokenURI);
    }
}

Build smart contract
Now the NFT smart contract is ready, let's compile it.
```
truffle compile
```
If the contract compiles successfully, related manifest files will be generated in build/contracts, which we will use later in this tutorial. (Tip: If you get a solidity compiler version incompatibility error, we can configure it in truffle.js to use the right compiler version.)
Create deployment script
Next, we need to to deploy the Solidity contract to the Harmony blockchain. Create a file named 2_deploy_contracts.js under migrations folder with the following code:
```
var HarmonyNft = artifacts.require("HarmonyNFT");

module.exports = function(deployer) {
  deployer.deploy(HarmonyNft);
};
```

Deploy NFT contract to Harmony Testnet

In order to deploy the NFT smart contract to Harmony Testnet, you need to let Truffle which network configuration and which Harmony wallet to use. You can do this by configuring truffle in truffle-config.js.

First, install @truffle/hdwallet-provider via npm.

npm install --save-dev @truffle/hdwallet-provider

Add harmony testnet configuration to truffle-config.js file. Also make sure requesting some TestNet token (ONE) from Harmony TestNet Faucet to the wallet so we can pay for transaction fees for smart contract deployment.

const HDWalletProvider = require('@truffle/hdwallet-provider');
//If you have a Harmony wallet in MetaMask, you can export the private key.
const privateKeyTest = '<ADD-YOUR-PRIVATE-KEY-HERE>';

....<other code>....
networks: {
    harmonyTestnet: {
      provider: () => {
        if (!privateKeyTest.trim()) {
          throw new Error(
            'Please enter a private key with funds, you can use the default one'
          );
        }
        return new HDWalletProvider({
          privateKeys: [privateKeyTest],
          providerOrUrl: 'https://api.s0.b.hmny.io',
        });
      },
      network_id: 1666700000,
    },
  },
... <other code>...

Now the truffle configuration is all set, we can run the following command to deploy the NFT contract to Harmony Testnet.

truffle deploy --network harmonyTestnet

Once the smart contract is deployed success, remember to record your smart contract address which we will also use later. You can also find your NFT contract on Harmony Testnet blockchain explorer, also test it on Remix.

Part 2: Connect to Metamask

In this step, we will write some front-end code to connect to a MetaMask wallet so that you can use it to mint the NFT and pay transaction fees.

Before we move forward, make sure we have installed MetaMask browser extension and add Harmony Network RPC Endpoint (we will use Harmony Testnet in this tutorial). Check more instructions here.

Now, let's start coding.

Create a WalletConnect component

This component will detect the wallet provider and connect to MetaMask. Go to the harmony-nft/src folder which was created as part of your React app in Part 1.

Within harmony-nft/src, create a new folder components. Inside components, create a WalletConnect.js file and paste in the following code:

Also make sure requesting some TestNet token (ONE) from Harmony TestNet Faucet to the wallet so we can pay for transaction fees for minting NFT on Harmony Blockchain.

//The core code to detect wallet provider and connect to MetaMask
const connectWalletHandler = async() => {
		if (window.ethereum && window.ethereum.isMetaMask) {
			console.log('MetaMask Here!');

			try {
				const accounts = await window.ethereum.request({ method: 'eth_requestAccounts'});
				accountChangedHandler(accounts[0]);
				setConnButtonText('Wallet Connected');
				setWalletConnected(true);
			} catch (error) {
				setErrorMessage(error.message);
			}

		} else {
            setWalletConnected(false);
			console.log('Need to install MetaMask');
			setErrorMessage('Please install MetaMask browser extension to interact');
		}
	}

Add the WalletConnect component to App.js

import WalletConnect from './components/WalletConnect'
...<other code>...
function App() {
  return (
    <div className='App'>
      <div className='logos'>
        <img className='harmony' src={harmonyLogo} alt="Harmony Logo"/>
        <img className='nftStorage' src={nftStorageLogo} alt="Harmony Logo"/>
      </div>
      <WalletConnect/>
    </div>
  );
}

Now, let's test the wallet connection function. Run the following command to start the React application.

npm start

Once the application is up, you can click the Connect Wallet button to invoke the MetaMask and authorize the connection.

Part 3: MintNFT process

In this step, we will write the code that mints the NFT. Have the following items ready:

NFT Smart Contract deployed to Harmony Testnet.
- NFT contract address
- NFT contract manifest JSON file
Metamask browser extension installed and filled your wallet with some TestNet token - ONE.

In this step, we will write code to mint a NFT on Harmony blockchain and also upload your NFT asset and metadata to IPFS & Filecoin so that your NFT is truly decentralized other than storing on centralized cloud. Here, we will use a tool called NFT.Storage which offers free and long-term storage on IPFS and Filecoin.

Create a NFT.Storage account.
In order to use NFT.Storage to upload NFT assets, we will need to sign up an account and create a new API Key which will be used in our code to access NFT.Storage services.
Also we will use ethers to interact with MetaMask to invoke NFT smart contract which is deployed on Harmony blockchain.

Create mintNFT component

Now we will create a MintNFT.js component in src/components folder. Let's first create a form to upload NFT Images in MintNFT.js.

import React, {useState} from 'react';
const MintNFT =() => {
  const [uploadedFile, setUploadedFile] = useState();

  const handleFileUpload = (event) => {
      setUploadedFile(event.target.files[0]);
  }

  const mintNFTToken = async(inputFile) =>{
      //Will add MintNFT logic here.
  }

  return(
      <div className='MintNFT'>
          <form>
              <h3>Mint your NFT on Harmony & Filecoin/IPFS</h3>
              <input type="file" onChange={handleFileUpload}></input>
              <button onClick={e=>mintNFTToken(e, uploadedFile)}>Mint NFT</button>
          </form>
      </div>
  )
}
export default MintNFT;

Once the NFT image is captured via form upload, we will upload the NFT asset and metadata to IPFS/Filecoin via NFT.storage, then invoke the NFT smart contract on Harmony to mint a new item. The basic logic will be like following:

const mintNFTToken = async(event, uploadedFile) =>{
    //1. Upload NFT content via NFT.storage
    const metaData = await uploadNFTContent(uploadedFile);

    //2. Mint a NFT token on Harmony
    const mintNFTTx = await sendTxToHarmony(metaData);
}

Upload NFT asset via NFT.Storage

Now let's set up NFT.Storage so you can upload NFT assets.

Install NFT.Storage dependency in your React app.
```
npm install nft.storage
```
We are all set to start coding your logic. Add the following code blocks to MintNFT.js. (You can also copy the entire sample file from Github.)

First, import NFTstorage and get the API Key that we created in the first step.

import { NFTStorage } from "nft.storage";
const APIKEY = '<Your-API-KEY>';
...

Then, initialize the NFTStorage connection using your API KEY.

const uploadNFTContent = async(inputFile) =>{
	//Initialize NFTStorage
    const nftStorage = new NFTStorage({token: APIKEY,});
}

We can simply call nftStorage.store() to upload NFT content, which will upload your NFT as well as its related metadata to IPFS & Filecoin. You can customize your NFT metadata by updating properties like name and description.

const uploadNFTContent = async(inputFile) =>{
    //Initialize NFTStorage
    const nftStorage = new NFTStorage({token: APIKEY,});
    try {
        //Upload NFT to IPFS & Filecoin
        const metadata = await nftStorage.store({
            name: 'Harmony NFT collection',
            description: 'This is a Harmony NFT collenction stored on IPFS & Filecoin.',
            image: file
        });
        return metadata;

    } catch (error) {
        setErrorMessage("Could not save NFT to NFT.Storage - Aborted minting.");
        console.log(error);
    }
}

If NFT asset is uploaded successfully, NFT.Storage will do the following two things:

Store NFT image on IPFS & Filecoin.
Update NFT metadata with the IPFS link to your NFT image, then also store the NFT metadata on IPFS & Filecoin.

Mint a new NFT on Harmony

After getting the metadata on IPFS, we can invoke the NFT smart contract on Harmony to mint a new NFT using that metadata as tokenURI.

In this step, we will need to use ethers to interact with Metamask, so we first install this dependency.

npm install ethers

In order to invoke the NFT contract we have deployed to Harmony Testnet, we need to grab the contract ABI from the manifest JSON file which was generated via smart contract compilation.

//run this command under harmony-nft folder
cp ../build/contracts/HarmonyNFT.json src/abi/

Then we are ready to write code to send MintNFT transaction in MintNFT.js . This will import ethers and the smart contract manifest file, and also create a nftContractAddress for the deployed NFT contract.

import HarmonyNFT from "../abi/HarmonyNFT.json";
import { ethers } from 'ethers';

const nftContractAddress = '0x494543afa8445025B9dBc7a39EdC7Fc624cA46F6';

Then we can load the deployed NFT contract and invoke mintItem method.

//Add this code to load deployed NFT contract and invoke mintItem method.
const sendTxToHarmony = async(metadata) =>{
    try {
        const provider = new ethers.providers.Web3Provider(window.ethereum);
        const connectedContract = new ethers.Contract(
            nftContractAddress,
            HarmonyNFT.abi,
            provider.getSigner()
        );
        const mintNFTTx = await connectedContract.mintItem(metadata.url);
        console.log(mintNFTTx);
    } catch (error) {
        setErrorMessage("Failed to send tx to Harmony.");
        console.log(error);
    }
}

Preview the new minted NFT

By now, we have all the codes to upload NFT data, send mint item transaction to Harmony. If everything works as expected, we will be able to mint a fresh NFT with its images and metadata stored on IPFS & Filecoin, minting transaction recorded on Harmony Blockchain. Let's add some code to preview our fresh minted NFT, including the NFT image, NFT metadata on IPFS and mintNFT transaction on Harmony.

const MintNFT =() => {
  ...
      const [imageView, setImageView] = useState();
      const [metaDataURL, setMetaDataURl] = useState();
      const [txURL, setTxURL] = useState();
      const [txStatus, setTxStatus] = useState();
  ...
  const mintNFTToken = async(inputFile) =>{
      ...
      //3. review your nft
      previewNFT(metaData, mintNFTTx);
  }
  ...
  const previewNFT = (metaData, mintNFTTx) =>{
      let imgViewString = getIPFSGatewayURL(metaData.data.image.pathname);;
      setImageView(imgViewString);
      setMetaDataURl(getIPFSGatewayURL(metaData.url));
      setTxURL('https://explorer.pops.one/tx/'+ mintNFTTx.hash);
      setTxStatus("NFT is minted successfully!");
  }

  //
  const getIPFSGatewayURL = (ipfsURL)=>{
      let urlArray = ipfsURL.split("/");
      let ipfsGateWayURL = `https://${urlArray[2]}.ipfs.dweb.link/${urlArray[3]}`;
      return ipfsGateWayURL;
  }
  ...
  return(
      <div className='MintNFT'>
          <form>
              <h3>Mint your NFT on Harmony & Filecoin/IPFS</h3>
              <input type="file" onChange={handleFileUpload}></input>
              <button onClick={e=>mintNFTToken(e)}>Mint NFT</button>
          </form>
          {errorMessage}
          {txStatus && <p>{txStatus}</p>}
          {imageView && <img className='NFTImg' src={imageView} alt="NFT image preview"/>}
          {metaDataURL && <p><a href={metaDataURL}>Metadata on IPFS</a></p>}
          {txURL && <p><a href={txURL}>See the mint transaction</a></p>}
      </div>
  )
}

You can find the full MintNFT.js file on Github.

Let's run it

Now that we've finished writing all the code, we can run npm start to start our React application. If everything is working, you should see a page like this:

Once we connect to MetaMask and upload a image to mint NFT, we will need to sign the transaction via MetaMask. Then a new NFT on Harmony is minted. We can also check the NFT metadata on IPFS and the minting transaction on Harmony Testnet.

Congratulations! You have written a simple React app for minting NFTs on Harmony with storage on IPFS and Filecoin. Feel free to explore more possibilities.

Looking for the sample code from this tutorial? You can find it in the harmony-nft-demo Github repo.

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