FlashLoan的实现过程

闪电贷主要由借贷方和放贷方两部分构成，放贷方部署放贷合约，借贷方部署借贷合约，通过借贷合约去调用放贷合约实现，大致流程如下图。

这里我们使用aave https://docs.aave.com/developers/guides/flash-loans 的实现来跟踪一下flashloan的过程，代码如下，aave这里没有使用标准的IERC3156实现，但是只需要将POOL.flashLoanSimple带入flashLoan、executeOperation带入onFlashLoan即可，其它流程基本一致。

// SPDX-License-Identifier: MIT
pragma solidity 0.8.10;

import "https://github.com/aave/aave-v3-core/blob/master/contracts/flashloan/base/FlashLoanSimpleReceiverBase.sol";
import "https://github.com/aave/aave-v3-core/blob/master/contracts/interfaces/IPoolAddressesProvider.sol";
import "https://github.com/aave/aave-v3-core/blob/master/contracts/dependencies/openzeppelin/contracts/IERC20.sol";


contract SimpleFlashLoan is FlashLoanSimpleReceiverBase {
    address payable owner;

    constructor(address _addressProvider)
        FlashLoanSimpleReceiverBase(IPoolAddressesProvider(_addressProvider))
    {
    }

    function fn_RequestFlashLoan(address _token, uint256 _amount) public {
        address receiverAddress = address(this);
        address asset = _token;
        uint256 amount = _amount;
        bytes memory params = "";
        uint16 referralCode = 0;

        POOL.flashLoanSimple(
            receiverAddress,
            asset,
            amount,
            params,
            referralCode
        );
    }


    /**
        This function is called after your contract has received the flash loaned amount
     */
    function  executeOperation(
        address asset,
        uint256 amount,
        uint256 premium,
        address initiator,
        bytes calldata params
    )  external override returns (bool) {
        
        //Logic goes here
        
        uint256 totalAmount = amount + premium;
        IERC20(asset).approve(address(POOL), totalAmount);

        return true;
    }

    receive() external payable {}
}

首先部署在Remix上部署合约，这里用的是Polygon Munbai的测试环境，所以在文档https://docs.aave.com/developers/deployed-contracts/v3-testnet-addresses 中找到aave对应的测试合约地址0xeb7A892BB04A8f836bDEeBbf60897A7Af1Bf5d7F作为初始参数传入部署合约

从上述的合约代码中可以看到，fn_RequestFlashLoan的入参分别是放贷地址以及借贷数量，同理，在aave的文档中找到usdc的金库地址0xe9DcE89B076BA6107Bb64EF30678efec11939234作为入参传入，发起借贷

在一切顺利的情况下，fn_RequestFlashLoan中调用POOL.flashLoanSimple发起借贷，在POOL.flashLoanSimple中放款并回调executeOperation

回调到借贷合约的executeOperation中后，执行预定的套利逻辑等一系列操作，然后返回状态通知executeFlashLoanSimple进行判断是否还款。

参考：https://github.com/quiknode-labs/qn-guide-examples/tree/main/ethereum/aave-flash-loan