daofi-metatx

eth-permit

This package simplifies the process of signing permit messages for Ethereum tokens.

What is permit?

Permit is a technique for metatransaction token transfers. Using permit can allow a contract to use a user's tokens without the user first needing to first to send an approve() transaction.

Permit variations

Permit was first introduced in the Multi-Collateral Dai token contract.

The permit technique is being standardized as part of ERC-2612. This standard (which has already been implemented in projects like Uniswap V2) is slightly different than the implementation used by Dai. Therefore, this library provides functions for signing both types of messages.

Usage

Install the package eth-permit using npm or yarn.

Dai-style permits

import { signDaiPermit } from 'eth-permit';

// Sign message using injected provider (ie Metamask).
// You can replace window.ethereum with any other web3 provider.
const result = await signDaiPermit(window.ethereum, tokenAddress, senderAddress, spender);

await token.methods.permit(senderAddress, spender, result.nonce, result.expiry, true, result.v, result.r, result.s).send({
  from: senderAddress,
});

ERC2612-style permits

import { signERC2612Permit } from 'eth-permit';

const value = web3.utils.toWei('1', 'ether');

// Sign message using injected provider (ie Metamask).
// You can replace window.ethereum with any other web3 provider.
const result = await signERC2612Permit(window.ethereum, tokenAddress, senderAddress, spender, value);

await token.methods.permit(senderAddress, spender, value, result.deadline, result.v, result.r, result.s).send({
  from: senderAddress,
});