Flash Loan

The lisUSD CDP is being wound down — see Mechanics for the live gates. Flash minting still works, so an existing integration keeps running. New integrations should use Lista Lending, whose Moolah.flashLoan is in the contract reference.

flash.sol is a standard ERC-3156 flash minter: it mints lisUSD to your contract, calls you back, and burns it again at the end of the same transaction. There is no collateral and no position — if the loan plus fee is not returned before the call ends, everything reverts.

Mainnet lender: 0x64d94e715B6c03A5D8ebc6B2144fcef278EC6aAa (FlashMinter on the Smart Contract page)

The interface

function maxFlashLoan(address token) external view returns (uint256);
function flashFee(address token, uint256 amount) external view returns (uint256);
function flashLoan(IERC3156FlashBorrower receiver, address token, uint256 amount, bytes calldata data) external returns (bool);

• token must be lisUSD. Anything else reverts Flash/token-unsupported; maxFlashLoan returns 0 for it.

• flashFee applies the toll rate and returns an 18-decimal wad.

• data is forwarded verbatim to your callback — it is the only channel for passing state in.

Writing the borrower

Implement IERC3156FlashBorrower and do three things in onFlashLoan: reject callers that are not the lender, run your logic, and approve the lender for amount + fee before returning keccak256("ERC3156FlashBorrower.onFlashLoan").

pragma solidity ^0.8.10;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "../interfaces/IERC3156FlashBorrower.sol";
import "../interfaces/IERC3156FlashLender.sol";

contract FlashBorrower is IERC3156FlashBorrower {
    IERC3156FlashLender lender;

    constructor(IERC3156FlashLender lender_) {
        lender = lender_;
    }

    function flashBorrow(address token, uint256 amount) public {
        bytes memory data = abi.encode(/* your parameters */);
        lender.flashLoan(this, token, amount, data);
    }

    function onFlashLoan(
        address initiator,
        address token,
        uint256 amount,
        uint256 fee,
        bytes calldata data
    ) external override returns (bytes32) {
        require(msg.sender == address(lender), "untrusted lender");
        require(initiator == address(this), "untrusted initiator");

        // ... your logic. It must leave this contract holding `amount + fee`.

        IERC20(token).approve(address(lender), amount + fee);
        return keccak256("ERC3156FlashBorrower.onFlashLoan");
    }
}

Return anything other than that hash and the call reverts Flash/callback-failed. Skip the approve, or end the callback short of amount + fee, and the lender's transferFrom reverts LisUSD/insufficient-allowance or LisUSD/insufficient-balance.

Flash loans cannot bid on CDP liquidations. This fork makes the auction buy side permissioned — Clipper.take / redo are auth and Interaction.buyFromAuction is whitelisted. The liquidation surface that is open to third parties is on Lista Lending: see Liquidator Integration.

Source

• flash.sol — the lender, including the max ceiling and toll rate.

• flashBorrower.sol — a fuller borrower, with branching on the decoded data.

• flash.test.js — a worked end-to-end example.