feat: 5.1 done

solidity/contracts/Flashloan/Flashloan.sol

@@ -0,0 +1,75 @@
+pragma solidity ^0.8.19;
+
+import {IERC20} from '@openzeppelin/contracts/token/ERC20/IERC20.sol';
+import {SafeERC20} from '@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol';
+import {IReceiver} from '../../interfaces/Flashloan/IReceiver.sol';
+import {IFlashloan} from '../../interfaces/Flashloan/IFlashloan.sol';
+import {ReentrancyGuard} from '@openzeppelin/contracts/utils/ReentrancyGuard.sol';
+
+// Without reentrancy guard, user can make a flashloan attack by using his flashloan to deposit into the pool
+contract Flashloan is IFlashloan, ReentrancyGuard {
+  using SafeERC20 for IERC20;
+
+  mapping(address _user => mapping(address _token => uint256 _amount)) tokenBalances;
+  mapping(address _user => uint256 _amount) ethBalances;
+
+  constructor() {}
+
+  /// @dev allows users to flashloan any tokens or eth deposited in the pool
+  /// @dev If address(0) is passed as _token, this is treated as ETH
+  /// @param _amount flashloan total desired, must not exceed pool balance
+  /// @param _token token (or eth) to be flashloaned
+  function flashloan(uint256 _amount, address _token) external nonReentrant {
+    if (address(_token) == address(0)) {
+      uint256 poolBalance = address(this).balance;
+      if (_amount > poolBalance) revert InsufficientPoolBalance();
+
+      IReceiver(msg.sender).getETH{value: _amount}();
+
+      uint256 balanceAfter = address(this).balance;
+
+      if (balanceAfter < poolBalance + (poolBalance * 1e13) / 1e18) revert InsufficientRepayment();
+    } else {
+      uint256 poolBalance = IERC20(_token).balanceOf(address(this));
+      if (_amount > poolBalance) revert InsufficientPoolBalance();
+
+      IERC20(_token).safeTransfer(msg.sender, _amount);
+      IReceiver(msg.sender).getTokens(_token, _amount);
+
+      uint256 balanceAfter = IERC20(_token).balanceOf(address(this));
+
+      if (balanceAfter < poolBalance + (poolBalance * 1e13) / 1e18) revert InsufficientRepayment();
+    }
+  }
+
+  /// @dev Deposit function for erc20 tokens or eth
+  /// @dev if _token address is address(0), this is an eth deposit
+  /// @param _amount Amount of token to deposit
+  /// @param _token Address of token to deposit
+  function deposit(uint256 _amount, address _token) external payable nonReentrant {
+    if (_token == address(0)) {
+      ethBalances[msg.sender] += msg.value;
+    } else {
+      IERC20(_token).safeTransferFrom(msg.sender, address(this), _amount);
+      tokenBalances[msg.sender][_token] += _amount;
+    }
+  }
+
+  /// @dev Withdraw function for erc20 tokens or eth
+  /// @dev if _token address is address(0), this is an eth withdrawal
+  /// @param _amount Amount of token to withdraw
+  /// @param _token Address of token to withdraw
+  function withdraw(uint256 _amount, address _token) external nonReentrant {
+    if (_token == address(0)) {
+      ethBalances[msg.sender] -= _amount;
+      (bool success,) = payable(msg.sender).call{value: _amount}('');
+      require(success, 'Failed to send ETH');
+    } else {
+      tokenBalances[msg.sender][_token] -= _amount;
+      IERC20(_token).safeTransfer(msg.sender, _amount);
+    }
+  }
+
+  /// @dev users can deposit eth by sending it directly to the contract
+  receive() external payable {}
+}

solidity/contracts/Flashloan/GreedyReceiver.sol

@@ -0,0 +1,30 @@
+pragma solidity ^0.8.19;
+
+import {IFlashloan} from '../../interfaces/Flashloan/IFlashloan.sol';
+import {IERC20} from '@openzeppelin/contracts/token/ERC20/IERC20.sol';
+import {SafeERC20} from '@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol';
+
+error OnlyPool();
+
+contract GreedyReceiver {
+  IFlashloan public pool;
+
+  using SafeERC20 for IERC20;
+
+  modifier onlyPool() {
+    if (msg.sender != address(pool)) revert OnlyPool();
+    _;
+  }
+
+  constructor(address _poolAddress) {
+    pool = IFlashloan(_poolAddress);
+  }
+
+  function flashLoan(uint256 _amount, address _token) external {
+    pool.flashloan(_amount, _token);
+  }
+
+  function getETH() external payable onlyPool {}
+
+  function getTokens(address _token, uint256 _amount) external onlyPool {}
+}

solidity/contracts/Flashloan/Receiver.sol

@@ -0,0 +1,35 @@
+pragma solidity ^0.8.19;
+
+import {IFlashloan} from '../../interfaces/Flashloan/IFlashloan.sol';
+import {IERC20} from '@openzeppelin/contracts/token/ERC20/IERC20.sol';
+import {SafeERC20} from '@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol';
+
+error OnlyPool();
+
+contract Receiver {
+  IFlashloan public pool;
+
+  using SafeERC20 for IERC20;
+
+  modifier onlyPool() {
+    if (msg.sender != address(pool)) revert OnlyPool();
+    _;
+  }
+
+  constructor(address _poolAddress) {
+    pool = IFlashloan(_poolAddress);
+  }
+
+  function flashLoan(uint256 _amount, address _token) external {
+    pool.flashloan(_amount, _token);
+  }
+
+  function getETH() external payable onlyPool {
+    (bool success,) = payable(msg.sender).call{value: msg.value + (msg.value * 1e13) / 1e18}('');
+    require(success, 'failed to send ETH');
+  }
+
+  function getTokens(address _token, uint256 _amount) external onlyPool {
+    IERC20(_token).safeTransfer(msg.sender, _amount + (_amount * 1e13) / 1e18);
+  }
+}