cyotee/permit2-signature-transfer-contract

Permit2 Signature Transfer - Contract Integration

Solidity implementation for permitWitnessTransferFrom pattern.

Contract Setup

import {ISignatureTransfer} from "@uniswap/permit2/src/interfaces/ISignatureTransfer.sol";

contract IndexedexRouter {
    address public constant PERMIT2 = 0x000000000022D473030F116dDEE9F6B43aC78BA3;

    // Must match frontend exactly
    string public constant WITNESS_TYPE_STRING =
        "PermitWitnessTransferFrom(TokenPermissions permitted,address spender,uint256 nonce,uint256 deadline,Witness witness)"
        "TokenPermissions(address token,uint256 amount)"
        "Witness(bytes32 actionId)";

    bytes32 public constant WITNESS_TYPEHASH = keccak256("Witness(bytes32 actionId)");
}

Exchange In Handler

function handlePermitSignatureIn(
    ISignatureTransfer.PermitTransferFrom calldata permit,
    ISignatureTransfer.SignatureTransferDetails calldata transferDetails,
    address owner,
    bytes32 actionId,
    bytes calldata signature
) external {
    bytes32 witness = keccak256(abi.encode(WITNESS_TYPEHASH, actionId));

    ISignatureTransfer(PERMIT2).permitWitnessTransferFrom(
        permit,
        transferDetails,
        owner,
        witness,
        WITNESS_TYPE_STRING,
        signature
    );

    // tokens now in this contract - execute the swap
}

Exchange Out Handler

For exact-out swaps, include maxAmountIn in the actionId:

bytes32 actionId = keccak256(abi.encodePacked(
    tokenIn,
    tokenOut,
    vaultAddress,
    amountOut,
    maxAmountIn
));

Cross-Chain Considerations

• Permit2 address is canonical (same on all chains)
• ChainId must match the network where signature will be used
• Signatures are not valid across chains