permit.md

Smart Contract Permit Function Tutorial

Developers should use ERC-2612 Permit instead of ERC-20 Approve because it allows for gasless token approvals through off-chain signatures, eliminating the need for a separate on-chain approval transaction. This not only reduces transaction costs but also streamlines user experience by enabling approvals and transfers to happen in a single transaction. By using Permit, developers can create more efficient and user-friendly applications, enhancing security and flexibility within the Ethereum ecosystem.

This tutorial breaks down the use of the permit function into digestible steps.

Step 1: Import Required Modules

Import the SigningKey module to sign the permit digest.

const { SigningKey } = require("@ethersproject/signing-key");

Step 2: Instantiate the Smart Contract Instances

Create instances of the smart contracts by using the ABI and address. Obtain the controller address through the instantiated EUR contract.

const { ethers } = require("ethers");

// EUR contract instantiation
const tokenABI = [...] // token ABI goes here
const tokenProxyAddress = "<token_proxy_contract_address>";
const token = new ethers.Contract(tokenProxyAddress, tokenABI, signer);

Step 3: Prepare the Permit Details

Define the nonce and deadline for the permit function.

const nonce = await token.nonce(<yourAddress>);
const deadline = Math.floor(Date.now() / 1000) + 60 * 60; // 1 hour from now

Step 4: Create the Permit Digest

Generate the digest that the permit function will use for transaction verification.

const digest = await token.getPermitDigest(
  <yourAddress>,
  <spenderAddress>,
  <value>,
  nonce,
  deadline
);

Step 5: Sign the Digest

Use your private key to sign the digest. This signature proves that you have authorized the transaction.

const signingKey = new SigningKey(<yourPrivateKey>);
const signature = signingKey.signDigest(digest);

Step 6: Submit the Permit Transaction

Complete the process by submitting the permit function with the required parameters and the signature.

await token.permit(
  <yourAddress>,
  <spenderAddress>,
  <value>,
  <deadline>,
  signature.v,
  signature.r,
  signature.s
);

Full Code

const { ethers } = require("ethers");
const { SigningKey } = require("@ethersproject/signing-key");

// Replace the following with your contract's ABI and addresses
const tokenABI = [...] // token ABI goes here
const tokenProxyAddress = "<token_proxy_contract_address>"; // token Proxy contract address
const rpc = "http://<your_rpc>"

async function permitFunction(yourAddress, spenderAddress, value, yourPrivateKey) {
  // Provider and signer would be set up here (e.g., using ethers.js)
  const provider = new ethers.providers.JsonRpcProvider(rpc);
  const signer = new ethers.Wallet(yourPrivateKey, provider);

  // Instantiate the contracts
  const token = new ethers.Contract(tokenProxyAddress, tokenABI, signer);

  // Prepare the permit details
  const nonce = await token.nonce(yourAddress);
  const deadline = Math.floor(Date.now() / 1000) + 60 * 60; // 1 hour from now

  // Create the permit digest
  const digest = await token.getPermitDigest(
    yourAddress,
    spenderAddress,
    value,
    nonce,
    deadline
  );

  // Sign the digest
  const signingKey = new SigningKey(yourPrivateKey);
  const signature = signingKey.signDigest(digest);

  // Submit the permit transaction
  const tx = await token.permit(
    yourAddress,
    spenderAddress,
    value,
    deadline,
    signature.v,
    signature.r,
    signature.s
  );

  return tx;
}

// Usage: call permitFunction with the required parameters
// permitFunction(<yourAddress>, <spenderAddress>, <value>, <yourPrivateKey>).then(...);