permit.md

Smart Contract Permit Function Tutorial

The permit function allows a spender to transfer tokens on behalf of the token holder with a signed permission. This tutorial breaks down the use of the permit function into digestible steps.

Step 1: Import Required Modules

Import the SigningKey module for signing 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 eurABI = [...] // EUR ABI goes here
const eurAddress = "<eur_contract_address>";
const eurContract = new ethers.Contract(eurAddress, eurABI, signer);

// Fetch the controller address from the EUR contract
const ctrlAddress = await eurContract.getController();

// Controller contract instantiation
const controllerABI = [...] // SmartController ABI goes here
const controller = new ethers.Contract(ctrlAddress, controllerABI, signer);

Step 3: Prepare the Permit Details

Define the nonce and deadline for the permit function.

const nonce = await controller.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 controller.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 controller.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 eurABI = [...] // EUR ABI goes here
const eurAddress = "<eur_contract_address>"; // EUR contract address
const controllerABI = [...] // SmartController ABI goes here

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("http://localhost:8545");
  const signer = new ethers.Wallet(yourPrivateKey, provider);

  // Instantiate the contracts
  const eurContract = new ethers.Contract(eurAddress, eurABI, signer);
  const ctrlAddress = await eurContract.getController();
  const controller = new ethers.Contract(ctrlAddress, controllerABI, signer);

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

  // Create the permit digest
  const digest = await controller.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 controller.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(...);