ERC3156Borrower

Universal adapter for flash loan providers implementing the ERC-3156 standard

Overview

The ERC3156Borrower contract enables the FlashLoanRouter to request flash loans from any lender implementing the ERC-3156 standard. It provides a universal interface for flash loan providers that follow the standard, including Maker’s Flash Mint Module.

Contract Details

• Source: src/ERC3156Borrower.sol
• License: GPL-3.0-or-later
• Solidity: ^0.8.28
• Address: 0x47d71b4B3336AB2729436186C216955F3C27cD04 (all networks)
• Inherits: Borrower, IERC3156FlashBorrower

Compatible Lenders

The ERC3156Borrower works with any lender implementing the ERC-3156 standard, including:

• Maker’s Flash Mint Module
• Yield Protocol
• Euler Finance
• Any other ERC-3156 compliant lender

Functions

flashLoanAndCallBack

function flashLoanAndCallBack(
    address lender,
    IERC20 token,
    uint256 amount,
    bytes calldata callBackData
) external onlyRouter

Initiates a flash loan request to an ERC-3156 compliant lender. Only callable by the registered router.

Parameters:

• lender: Address of the ERC-3156 flash loan provider
• token: ERC-20 token to borrow
• amount: Amount of tokens to borrow
• callBackData: Data to pass back to the router unchanged

onFlashLoan

function onFlashLoan(
    address initiator,
    address token,
    uint256 amount,
    uint256 fee,
    bytes calldata data
) external returns (bytes32)

ERC-3156 callback invoked by the lender after transferring borrowed funds. Notifies the router and returns the required success constant.

Parameters:

• initiator: Address that initiated the flash loan
• token: Address of the borrowed token
• amount: Amount borrowed
• fee: Fee charged by the lender
• data: Encoded callback data (passed through unchanged)

Returns: keccak256("ERC3156FlashBorrower.onFlashLoan") — the ERC-3156 success constant

approve

function approve(
    IERC20 token,
    address target,
    uint256 amount
) external onlySettlementContract

Allows the settlement contract to authorize token spending during settlement for repayment.

triggerFlashLoan (internal)

function triggerFlashLoan(
    address lender,
    IERC20 token,
    uint256 amount,
    bytes calldata callBackData
) internal override

Internal implementation that calls IERC3156FlashLender.flashLoan() and validates the result.

bool success = IERC3156FlashLender(lender).flashLoan(
    this,
    address(token),
    amount,
    callBackData
);
require(success, "Flash loan was unsuccessful");

Execution Flow

1. Router calls flashLoanAndCallBack() on the ERC3156Borrower
2. ERC3156Borrower calls IERC3156FlashLender.flashLoan() on the lender
3. Lender transfers the requested tokens to the ERC3156Borrower
4. Lender invokes onFlashLoan() on the ERC3156Borrower
5. ERC3156Borrower calls router.borrowerCallBack() to continue execution
6. ERC3156Borrower returns the success constant to the lender
7. During settlement, the settlement contract calls approve() for lender repayment
8. Lender pulls the borrowed amount plus fee via transferFrom()

Success Constant

The ERC-3156 standard requires the borrower to return a specific constant from onFlashLoan():

bytes32 private constant ERC3156_ONFLASHLOAN_SUCCESS =
    keccak256("ERC3156FlashBorrower.onFlashLoan");

Returning any other value will cause the lender to revert the transaction.

Security

• flashLoanAndCallBack(): Only callable by the registered router
• approve(): Only callable by the settlement contract
• onFlashLoan(): Called by the lender within the flash loan flow
• Validates flash loan success before proceeding
• Immutable router and settlement contract references

Always verify that the lender address is a legitimate ERC-3156 compliant contract. Query the lender’s flashFee() and maxFlashLoan() functions to verify fee structure and borrowing limits before use.

Integration Notes

• Fees vary by lender and asset — query flashFee() before constructing settlements
• Maximum loan amounts can be checked via maxFlashLoan()
• Some lenders may have specific token restrictions
• The settlement must include an interaction to approve the lender for repayment (principal + fee)

Next Steps

AaveBorrower

Aave flash loan adapter

Borrower Base

Abstract base contract