short-ans.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.8.1 <0.9.0;

/**
 * @dev
 * The original contract:
 * https://etherscan.io/address/0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2#code
 */
interface IWeth9 {
    function allowance(address, address) external returns (uint256);
    function deposit() external payable;
    function withdraw(uint256) external;
    function transferFrom(address, address, uint256) external returns (bool);
}

/**
 * @dev
 * This contract will deposit and withdraw eth through calling WETH contract
 */
contract ShortAns {
    IWeth9 immutable WETH;
    event Log(string event_msg);
    
    // The contructor argument must be the address of Wrapped Ether contract
    constructor(address payable _address) {
        WETH = IWeth9(_address);
    }
    
    function userDeposit() public payable returns (bool) {
        address user          = msg.sender;
        address this_contract = address(this);
        
        // Deposit eth
        try WETH.deposit{value: msg.value}() { // balanceOf[this_contract] += msg.value
            emit Log("Message call OK");
        }
        catch {
            emit Log("Message call failed: deposit()");
            return false;
        }
        
        // Transfer weth to msg.sender's address
        try WETH.transferFrom(this_contract, user, msg.value) {
            emit Log("Message call OK");
        }
        catch {
            emit Log("Message call failed: transferFrom()");
            return false;
        }
        
        return true;
    }
    
    function userWithdraw(uint256 amount) public returns (bool) {
        address user          = msg.sender;
        address this_contract = address(this);
        
        require(WETH.allowance(user, this_contract) >= amount, "Withdraw failed: you must approve enough allowance");
        
        // Transfer weth to this contract
        try WETH.transferFrom(user, this_contract, amount) {
            emit Log("Message call OK");
        }
        catch {
            emit Log("Message call failed: transferFrom()");
            return false;
        }
        
        // Withdraw weth
        try WETH.withdraw(amount) {
            emit Log("Message call OK");
        }
        catch {
            emit Log("Message call failed: withdraw()");
            return false;
        }
        
        // Send eth to msg.sender
        (bool ack, ) = payable(user).call{value: amount}("");
        
        return ack;
    }
}