Permit2 (permit2)

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When to use it

• Uniswap’s token-approval contract at one address on every chain it is on. A signature transfer (permitTransferFrom) moves a user’s tokens with a one-time signed permit; an allowance transfer (approve with an expiry, then transferFrom) works like an expiring ERC-20 allowance.
• sauce run --fund pulls with Permit2 by default: the owner signs, the Pot receives.

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Pitfalls for a program

• The user approves Permit2 itself once per token, by an ordinary ERC-20 approve.
• A signed permit names the spender (the contract calling Permit2: the Pot), the amount, a nonce and a deadline; nonces are unordered bits, each usable once.
• Allowance amounts are uint160 and expiries uint48.

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In a Sauce program

function main(
  owner: Address,
  token: Address,
  amount: Uint256,
  nonce: Uint256,
  deadline: Uint256,
  signature: bytes
) {
  const permit = { permitted: { token: token, amount: amount }, nonce: nonce, deadline: deadline };
  const details = { to: pot, requestedAmount: amount };
  const before = Token(token).balanceOf(pot);
  Permit2.Permit2.permitTransferFrom(permit, details, owner, signature);
  require(Token(token).balanceOf(pot) - before == amount, "the permit moved another amount");
}

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What it offers

• approve: Set token allowance for a spender via Permit2
• transferFrom: Transfer tokens using a Permit2 allowance

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Notes

• Same address on all 9 chains (deterministic CREATE2 deployment)
• Approve once: ERC-20 approve to Permit2, then use Permit2 to manage per-protocol allowances
• amount is uint160 (not uint256) - max value is type(uint160).max
• expiration is uint48 unix timestamp - approvals auto-expire for security
• Uniswap V3/V4, 1inch, and many protocols use Permit2 for token transfers
• lockdown is an emergency function to batch-revoke compromised approvals

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Its names in a program

function main() {
  // Ethereum's permit2, `0x000000000022D473030F116dDEE9F6B43aC78BA3`.
  require(Permit2.Permit2 != 0);
}

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Deployments

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ABI

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Permit2ABI

• approve(address token, address spender, uint160 amount, uint48 expiration)
• transferFrom(address from, address to, uint160 amount, address token)
• permitTransferFrom(((address token, uint256 amount) permitted, uint256 nonce, uint256 deadline) permit, (address to, uint256 requestedAmount) transferDetails, address owner, bytes signature)
• nonceBitmap(address owner, uint256 wordPosition) view returns (uint256)
• lockdown((address token, address spender)[] approvals)

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Next steps

• Protocols: the other protocols, by what they do.
• Protocols and tokens: calling a contract by its namespace, or through its ABI.
• Glossary: the words these pages use, in plain terms.