To implement EIP-2612 in a Next.js application, you need to handle both the off-chain signature creation and the on-chain execution of the permit function followed by the transferFrom. Below is a detailed step-by-step guide on how to achieve this using ethers.js in your Next.js app.

Step 1: Set Up the Next.js Project

Ensure your Next.js project is set up. If not, you can create one using:

npx create-next-app my-eip2612-app
cd my-eip2612-app

Step 2: Install Required Dependencies

Install ethers.js to interact with Ethereum blockchain:

npm install ethers

Step 3: Create a Permit Component

Create a Next.js component that will handle both the off-chain signing of the permit and the on-chain execution of permit and transferFrom.

Component Structure

Sign the Permit: This part is done off-chain by the token owner using their private key via a connected wallet like MetaMask.
Execute Permit and Transfer: This is done on-chain by the spender, which involves calling the permit function followed by the transferFrom function.

PermitComponent.js

Create a file named PermitComponent.js inside your components folder:

// components/PermitComponent.js
import { ethers } from "ethers";
import { useEffect, useState } from "react";

// Replace with the ABI of your ERC20 token with permit functionality
const ERC20_ABI = [
  "function permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s) external",
  "function transferFrom(address sender, address recipient, uint256 amount) external returns (bool)",
  "function nonces(address owner) external view returns (uint256)",
  "function DOMAIN_SEPARATOR() external view returns (bytes32)"
];

export default function PermitComponent() {
  const [provider, setProvider] = useState(null);
  const [signer, setSigner] = useState(null);
  const [owner, setOwner] = useState("");
  const [spender, setSpender] = useState("");
  const [value, setValue] = useState(0);
  const [deadline, setDeadline] = useState(Math.floor(Date.now() / 1000) + 3600); // 1 hour from now
  const [tokenAddress, setTokenAddress] = useState("0xYourTokenAddressHere"); // Replace with your token address

  useEffect(() => {
    // Initialize provider and signer when the component mounts
    const initializeProvider = async () => {
      if (window.ethereum) {
        const web3Provider = new ethers.providers.Web3Provider(window.ethereum);
        await web3Provider.send("eth_requestAccounts", []); // Request access to user accounts
        setProvider(web3Provider);
        const web3Signer = web3Provider.getSigner();
        setSigner(web3Signer);
        const accounts = await web3Provider.listAccounts();
        setOwner(accounts[0]);
      } else {
        console.error("Please install MetaMask!");
      }
    };

    initializeProvider();
  }, []);

  const handlePermitAndTransfer = async () => {
    try {
      if (!provider || !signer || !tokenAddress) {
        console.error("Provider, signer, or token address not set");
        return;
      }

      const tokenContract = new ethers.Contract(tokenAddress, ERC20_ABI, signer);
      const nonce = await tokenContract.nonces(owner);
      const domainSeparator = await tokenContract.DOMAIN_SEPARATOR();

      // EIP712 Domain and Permit Type Definitions
      const domain = {
        name: "My Token", // Replace with your token's name
        version: "1",
        chainId: (await provider.getNetwork()).chainId,
        verifyingContract: tokenAddress
      };

      const types = {
        Permit: [
          { name: "owner", type: "address" },
          { name: "spender", type: "address" },
          { name: "value", type: "uint256" },
          { name: "nonce", type: "uint256" },
          { name: "deadline", type: "uint256" }
        ]
      };

      const message = {
        owner,
        spender,
        value: ethers.utils.parseUnits(value.toString(), 18),
        nonce: nonce.toNumber(),
        deadline
      };

      // Sign the typed data
      const signature = await signer._signTypedData(domain, types, message);
      const { v, r, s } = ethers.utils.splitSignature(signature);

      // 1. Call permit function with the signed data
      const permitTx = await tokenContract.permit(owner, spender, message.value, deadline, v, r, s);
      await permitTx.wait(); // Wait for the permit transaction to be mined
      console.log("Permit transaction confirmed:", permitTx);

      // 2. Now call transferFrom to move the tokens
      const transferTx = await tokenContract.transferFrom(owner, spender, message.value);
      await transferTx.wait(); // Wait for the transfer transaction to be mined
      console.log("Transfer transaction confirmed:", transferTx);

      alert("Tokens successfully transferred!");
    } catch (error) {
      console.error("Error executing permit and transfer:", error);
    }
  };

  return (
    <div>
      <h1>EIP-2612 Permit and Transfer</h1>
      <input
        type="text"
        placeholder="Spender Address"
        value={spender}
        onChange={(e) => setSpender(e.target.value)}
      />
      <input
        type="number"
        placeholder="Amount"
        value={value}
        onChange={(e) => setValue(e.target.value)}
      />
      <button onClick={handlePermitAndTransfer}>Execute Permit and Transfer</button>
    </div>
  );
}

Step 4: Use the Permit Component in Your Application

You can now import and use the PermitComponent in your Next.js pages.

Example Usage in a Next.js Page

Create a file named index.js inside your pages folder:

// pages/index.js
import PermitComponent from "../components/PermitComponent";

export default function Home() {
  return (
    <div>
      <h1>Next.js EIP-2612 Implementation</h1>
      <PermitComponent />
    </div>
  );
}

Step 5: Run the Application

Run your Next.js application:

npm run dev

Explanation of Key Steps

Provider and Signer Initialization:
- A Web3 provider and signer are set up to interact with the blockchain using MetaMask.
Signature Creation (Off-Chain):
- The signer._signTypedData() method creates an EIP-712 compliant signature without spending gas, allowing the token owner to authorize the transfer off-chain.
Execution of permit and transferFrom (On-Chain):
- The permit transaction is submitted to the blockchain, granting approval.
- The transferFrom function is called immediately after, using the permit to transfer the tokens.

Considerations

Gas Costs: The spender (or anyone calling permit) will pay gas for the on-chain transactions.
Error Handling: Ensure proper error handling to manage failed transactions or signature errors.
Security: Ensure the signer correctly signs the permit and that domain data is accurate to avoid replay attacks.

This setup provides a practical way to leverage EIP-2612 in a Next.js application, enhancing user experience by reducing redundant on-chain transactions.

What is EIP2612 and How to Implement EIP2612 in NextJS?