The time lock Solidity smart contract below demonstrates how to use the passing of time in a Solidity smart contract. Think of this contract like a weekly allowance or escrow that needs to pay out weekly.
This contract makes use of:
- importing
- time
- mappings
- required functions
- etc
Experiment with the contract below and learn the basics of a simple contract. Deploy the contract below to the Ethereum test network using Remix. Try to add another function.
pragma solidity ^0.8.0;
// overflow and underflow examples and preventions
// one can deposit ether into this contract but you must wait 1 week before you can withdraw your funds
// use safe math to prevent underflow and overflow
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/math/SafeMath.sol";
contract Timelock {
// calling SafeMath will add extra functions to the uint data type
using SafeMath for uint; // you can make a call like myUint.add(123)
// amount of ether you deposited is saved in balances
mapping(address => uint) public balances;
// when you can withdraw is saved in lockTime
mapping(address => uint) public lockTime;
function deposit() external payable {
//update balance
balances[msg.sender] +=msg.value;
//updates locktime 1 week from now
lockTime[msg.sender] = block.timestamp + 1 weeks;
}
// the function that is commented out is vulnerable to overflow by updating the function below with a very large number
// to prevent this use safe math to prevent overflow
// function increaseLockTime(uint _secondsToIncrease) public {
// lockTime[msg.sender] += _secondsToIncrease;
// }
function increaseLockTime(uint _secondsToIncrease) public {
// the add function below is from safemath and will take care of uint overflow
// if a call to add causes an error an error will be thrown and the call to the function will fail
lockTime[msg.sender] = lockTime[msg.sender].add(_secondsToIncrease);
}
function withdraw() public {
// check that the sender has ether deposited in this contract in the mapping and the balance is >0
require(balances[msg.sender] > 0, "insufficient funds");
// check that the now time is > the time saved in the lock time mapping
require(block.timestamp > lockTime[msg.sender], "lock time has not expired");
// update the balance
uint amount = balances[msg.sender];
balances[msg.sender] = 0;
// send the ether back to the sender
(bool sent, ) = msg.sender.call{value: amount}("");
require(sent, "Failed to send ether");
}
}Try it in Remix
This code is for learning and entertainment purposes only. The time lock Solidity smart contract has not been audited. Use at your own risk. Remember smart contracts are experimental and could contain bugs.
Click here for more information about how to use the Ethereum test network and how to obtain test ETH.