ERC3156Borrower

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Overview

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Contract Details

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

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Compatible Lenders

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

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Functions

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flashLoanAndCallBack

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

• 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

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onFlashLoan

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

• 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)

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approve

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

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triggerFlashLoan (internal)

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

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

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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()

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Success Constant

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

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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

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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)

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Next Steps