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Overview

Flash loans let you borrow any amount of available liquidity from the Pool in a single transaction, as long as the borrowed amount (plus fee) is returned — or a debt position is opened — by the end of the transaction. No collateral is required. HypurrFi Pooled Markets support two flash loan variants:
MethodAssetsCan open debtFee waiver for FLASH_BORROWER
flashLoanMulti-assetYesYes
flashLoanSimpleSingle assetNoNo

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Fee Structure

Query the current flash loan premiums from the Pool contract: 
const pool = new ethers.Contract(POOL_ADDRESS, poolABI, provider);

// Total premium paid by borrower (in basis points, e.g., 5 = 0.05%)
const totalPremium = await pool.FLASHLOAN_PREMIUM_TOTAL();

// Portion of premium accrued to protocol treasury
const protocolPremium = await pool.FLASHLOAN_PREMIUM_TO_PROTOCOL();
The remainder (totalPremium - protocolPremium) is distributed to liquidity providers.
Flash loan fees are waived for addresses with the FLASH_BORROWER role (applies to flashLoan only, not flashLoanSimple). This role is granted via governance.

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IFlashLoanReceiver Interface

Your receiver contract must implement: 
interface IFlashLoanReceiver {
    function executeOperation(
        address[] calldata assets,
        uint256[] calldata amounts,
        uint256[] calldata premiums,
        address initiator,
        bytes calldata params
    ) external returns (bool);
}
ParameterDescription
assetsAddresses of the borrowed assets
amountsAmounts of each asset borrowed
premiumsFee amounts due for each asset
initiatorAddress that initiated the flash loan
paramsArbitrary bytes passed from the original flashLoan call
Your executeOperation must:
  1. Execute your logic (arbitrage, refinancing, etc.)
  2. Approve the Pool to pull back amounts[i] + premiums[i] for each asset
  3. Return true

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flashLoan (Multi-Asset)

function flashLoan(
    address receiverAddress,
    address[] calldata assets,
    uint256[] calldata amounts,
    uint256[] calldata modes,        // 0=no debt, 1=stable(N/A), 2=variable
    address onBehalfOf,
    bytes calldata params,
    uint16 referralCode              // use 0
) external
The modes array determines what happens if you don’t repay:
  • 0 — no debt position; you must repay amount + fee or the tx reverts
  • 2 — open a variable-rate debt position on onBehalfOf (who must have collateral and have delegated credit to msg.sender)
Mode 1 (stable debt) is not supported on HypurrFi.

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flashLoanSimple (Single Asset)

function flashLoanSimple(
    address receiverAddress,
    address asset,
    uint256 amount,
    bytes calldata params,
    uint16 referralCode              // use 0
) external
Simpler variant: single asset, no debt opening, no fee waiver.

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Solidity Example

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import {IPool} from "@aave/v3-core/contracts/interfaces/IPool.sol";
import {IFlashLoanReceiver} from "@aave/v3-core/contracts/flashloan/base/FlashLoanReceiverBase.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract MyFlashLoan is IFlashLoanReceiver {
    IPool public constant POOL = IPool(0xceCcE0EB9DD2Ef7996e01e25DD70e461F918A14b);

    function executeFlashLoan(address asset, uint256 amount) external {
        address[] memory assets = new address[](1);
        assets[0] = asset;
        uint256[] memory amounts = new uint256[](1);
        amounts[0] = amount;
        uint256[] memory modes = new uint256[](1);
        modes[0] = 0; // no debt

        POOL.flashLoan(
            address(this),
            assets,
            amounts,
            modes,
            address(this),
            "",    // params
            0      // referralCode
        );
    }

    function executeOperation(
        address[] calldata assets,
        uint256[] calldata amounts,
        uint256[] calldata premiums,
        address initiator,
        bytes calldata params
    ) external override returns (bool) {
        // --- Your logic here ---
        // e.g., arbitrage, collateral swap, refinancing

        // Approve repayment: amount + premium
        for (uint i = 0; i < assets.length; i++) {
            uint256 amountOwed = amounts[i] + premiums[i];
            IERC20(assets[i]).approve(address(POOL), amountOwed);
        }
        return true;
    }
}

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TypeScript Example (Calling an Existing Receiver)

const pool = new ethers.Contract(POOL_ADDRESS, poolABI, signer);

const tx = await pool.flashLoan(
  receiverContractAddress,
  [assetAddress],          // assets
  [ethers.parseUnits("1000", 6)], // amounts (e.g., 1000 USDC)
  [0],                     // modes (0 = no debt)
  signer.address,          // onBehalfOf
  "0x",                    // params
  0                        // referralCode
);
await tx.wait();

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References