Питання та відповіді експертів
Ставте питання експертам спільноти Solidity
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18- Питання та відповіді експертівMar 29, 2025
How to generate random Number between 1&2 without VRF?
So I was making a coinflip game which assigns head- 1 and tails -2 and when user places bet on polygon chain.... smart contract generates a random number between 1 and 2 and if the outcome is same...user gets double - (5 % as fee to the owner of contract) ! from a pool and if outcome is different then user loses all and the lost amount is deposited in the pool - (3% as fee to the owner) (to fund winners)... but any way to make genrate a random number? I have no funds at all so I can't afford chainlink VRF to generate. So is there any other secure way for this? plus I am pritty new to solidity so I made this code with help of chat gpt but I don't it works....can anyone help to make the code better? code- // SPDX-License-Identifier: MIT pragma solidity ^0.8.0; contract CoinFlip { address public owner; uint256 public contractBalance; event BetPlaced(address indexed player, uint256 amount, bool choice); event BetResult(address indexed player, uint256 amount, bool won); constructor() { owner = msg.sender; } function placeBet(bool choice) external payable { require(msg.value > 0, "Bet amount must be greater than 0"); bool outcome = (block.timestamp % 2 == 0); // Simple pseudo-random outcome if (outcome == choice) { uint256 winAmount = (msg.value * 2 * 95) / 100; require(address(this).balance >= winAmount, "Insufficient contract balance"); payable(msg.sender).transfer(winAmount); emit BetResult(msg.sender, winAmount, true); } else { uint256 lostAmount = (msg.value * 97) / 100; contractBalance += lostAmount; emit BetResult(msg.sender, msg.value, false); } emit BetPlaced(msg.sender, msg.value, choice); } function depositFunds() external payable { require(msg.sender == owner, "Only owner can deposit funds"); contractBalance += msg.value; } function withdrawFunds(uint256 amount) external { require(msg.sender == owner, "Only owner can withdraw funds"); require(amount <= address(this).balance, "Insufficient contract balance"); payable(owner).transfer(amount); contractBalance -= amount; } } `
- Smart Contract
- Solidity
01 - Питання та відповіді експертів
Jun 04, 2024How often does the solidity syntax change
I'd like to know how often the solidity syntax rules are changed and the best newsletter to follow up on the most recent updates
- Smart Contract
- Solidity
- Language Grammar
- Solidity Compiler
11 - Питання та відповіді експертівJan 09, 2024
Remix-like tool for Anvil
I know you can deploy contracts from Remix to Anvil. But is there a way to interact with contracts that were deployed from my machine in Anvil? These contracts are not visible in Remix. Or is there another tool like Remix that can do that? How are the experienced developers interacting with contracts? Thanks
- Solidity
11 - Питання та відповіді експертівNov 07, 2023
Solidity - Trouble Installing Foundry: SSL Connection Timeout"
I'm encountering an issue while trying to install Foundry using the command Dload Upload Total Spent Left Speed 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 0 0 0 0 0 0 0 0 --:--:-- 0:05:01 --:--:-- 0 curl: (28) SSL connection timeout
- Solidity
11 - Питання та відповіді експертівOct 23, 2023
Error when calling `increaseLiquidity ` in nonFungiblePositionManager.
I have failing tests when calling increaseLiquidity in nonFungiblePositionManager. decreaseLiquidity works as expected but increaseLiquidity is failing. This is the code: underlyingPositionManager.increaseLiquidity( INonfungiblePositionManager.IncreaseLiquidityParams({ tokenId: loan.tokenId, amount0Desired: amount0, amount1Desired: amount1, amount0Min: 0, amount1Min: 0, deadline: block.timestamp }) This is the foundry output for the test [12350] 0xC36442b4a4522E871399CD717aBDD847Ab11FE88::increaseLiquidity((512098 [5.12e5], 0, 671529 [6.715e5], 0, 0, 1685033235 [1.685e9])) │ │ ├─ [696] 0xCBCdF9626bC03E24f779434178A73a0B4bad62eD::slot0() [staticcall] │ │ │ └─ ← 0x000000000000000000000000000000000005db000f1598ba8f0e02e024506208000000000000000000000000000000000000000000000000000000000003ec8f000000000000000000000000000000000000000000000000000000000000006400000000000000000000000000000000000000000000000000000000000000c800000000000000000000000000000000000000000000000000000000000000c800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 │ │ ├─ [3747] 0xCBCdF9626bC03E24f779434178A73a0B4bad62eD::mint(0xC36442b4a4522E871399CD717aBDD847Ab11FE88, 253320, 264600, 0, 0x0000000000000000000000002260fac5e5542a773aa44fbcfedf7c193bc2c599000000000000000000000000c02aaa39b223fe8d0a0e5c4f27ead9083c756cc20000000000000000000000000000000000000000000000000000000000000bb80000000000000000000000002e234dae75c793f67a35089c9d99245e1c58470b) │ │ │ └─ ← "EvmError: Revert" │ │ └─ ← "EvmError: Revert" │ └─ ← "EvmError: Revert" └─ ← "EvmError: Revert" Test result: FAILED. 0 passed; 1 failed; 0 skipped; finished in 424.01ms Ran 1 test suites: 0 tests passed, 1 failed, 0 skipped (1 total tests) Can someone tell me what might be the issue, thank you.
- Smart Contract
- Solidity
01 - Питання та відповіді експертівfoufrix10Jul 31, 2023
Foundry cannot estimate gas price on Arbitrum
Hi, I'm trying to solve this CTF on Arbitrum: https://arbiscan.io/address/0xdF7cdFF0c5e85c974D6377244D9A0CEffA2b7A86#code The problem is okay to solve, but I'm having trouble sending the TX from Foundry to Arbitrum. Here is the code: // SPDX-License-Identifier: MIT pragma solidity 0.8.19; import {Script, console} from "forge-std/Script.sol"; interface Challenge { function solveChallenge(uint256 randomGuess, string memory yourTwitterHandle) external; } contract SolveChallenge is Script { Challenge challenge = Challenge(0xdF7cdFF0c5e85c974D6377244D9A0CEffA2b7A86); function run() external { vm.startBroadcast(vm.envUint("PRIVATE_KEY")); uint256 correctAnswer = uint256(keccak256(abi.encodePacked(msg.sender, block.prevrandao, block.timestamp))) % 100000; challenge.solveChallenge(correctAnswer, "foufrix"); vm.stopBroadcast(); } } I'm launching the script with this command: forge script script/SolveChallenge.s.sol:SolveChallenge --private-key $PRIVATE_KEY --rpc-url $RPC_URL --broadcast --skip-simulation -vvvvv Also tried with --with-gas-price 100000000 --gas-price 100000000 --gas-limit 3000000 The preview runs well, but It failed when trying to send the transaction to Arbitrum: Any idea on how to solve that? I tried different command from foundry that are suppose to manually set gas price but it does not seems to work. Note : could be nice to add the foundry tag :) (as well as hardhat & brownie)
- Smart Contract
- Solidity
01 - Питання та відповіді експертівJul 10, 2023
How to reverse keccak256 in solidity
I need help with the following code where I'm given the keccak256 of a parameter and need to reverse it to find the parameter to solve the challenge contract LessonFive is AFoundryCourseChallenge { error LessonFive__WrongPassword(); bytes32 public constant EXPECTED_BYTES = 0xb68fe43f0d1a0d7aef123722670be50268e15365401c442f8806ef83b612976b; /* CALL THIS FUNCTION! * Use all the help you can on this one! Google, AI, friends, peeranha, ethereum stack exchange, etc. * Hint: It's a very common... * @param password - A string that when you keccak256 it will return the EXPECTED_BYTES! @param yourTwitterHandle - Your twitter handle. Can be a blank string. */ function solveChallenge(string memory password, string memory yourTwitterHandle) external { if (keccak256(abi.encodePacked(password)) == EXPECTED_BYTES) { _updateAndRewardSolver(yourTwitterHandle); } else { revert LessonFive__WrongPassword(); } } } `
- Smart Contract
- Solidity
22 - Питання та відповіді експертівJun 29, 2023
The Trade functionality in my Solidity Contract is not Working
The Trade functionality in my Solidity Contract is not Working. Giving Error "Unknown error: "Execution reverted with reason: Pancake: TRANSFER_FAILED.". Try increasing your slippage tolerance.". It is Deployed in BSC Testnet. I am adding liquidity through PCS Router from BSCScan. Here is my code and it is under Development/ testing: ''' pragma solidity >=0.8.4 uint256) public balanceOf; mapping (address => mapping(address => uint256)) public Allowance; uint256 private BUY_TAX_RATE = 5; // 1% buy tax uint256 private SELL_TAX_RATE = 10; // 2% sell tax IRouter router; address pair; address[] WhiteListed; address public taxAddress = 0xE89145e7d9a9b6a4BCacb82659b8bE0e0fFC70A0; // Address where the tax amount will be deposited event Transfer(address indexed from, address indexed to, uint256 value); event Burn(address indexed from, uint256 value); event TransferOwnerShip(address indexed from,address indexed to); event Approval(address indexed owner, address indexed spender, uint value); //////////////////////////////////////////////////// constructor(address routerAddress) { IRouter _router = IRouter(routerAddress); address _pair = IFactory(_router.factory()).createPair(address(this), _router.WETH()); //create a pair with BNB router = _router; pair = _pair; balanceOf[msg.sender] = totalSupply; Owner = msg.sender; WhiteListed.push(Owner); } //////////////////////////////////////////////////// modifier onlyOwner { require(msg.sender == Owner, "Only Owner can call this Function"); _; } modifier Whitelisted { bool isWhiteListed = false; for(uint256 i = 0; i weth address[] memory path = new address; path[0] = address(this); path[1] = router.WETH(); Approve(address(router), tokenAmount); // make the swap try router.swapExactTokensForETHSupportingFeeOnTransferTokens( tokenAmount, 0, // accept any amount of ETH path, address(this), block.timestamp ) {} catch { return; } } function addLiquidity(uint256 tokenAmount, uint256 BNBamount) public Whitelisted payable { Approve(address(router), tokenAmount); try router.addLiquidityETH{value: BNBamount}( address(this), tokenAmount, 0, 0, Owner, block.timestamp + 1000 ){} catch {return;} } function WhiteListAddress(address Address_to_be_White_listed) public onlyOwner returns(string memory) { WhiteListed.push(Address_to_be_White_listed); return("Succesfully WhiteListed"); } function CheckWhiteListedAddress(address See_Address_to_be_WhiteListed) public view returns(bool isWhiteListed) { isWhiteListed = false; for(uint256 i = 0; i = value, 'balance too low'); //checks that balance of the address is greater or equal to value of the functiom require(Allowancefrom >= value, 'allowance too low'); uint256 _value = value * (10 ** decimals); balanceOf[to] += _value; //adds the amt of token to the recieve address balanceOf[from] -= _value; //subs the amt of token from the sender address emit Transfer(from, to, _value); //call the event } function transfer(address to, uint256 value) public { require(balanceOf[msg.sender] >= value, "Insufficient balance"); uint256 tax = 0; uint256 _value = value * (10 ** decimals); Approve(address(router), _value); if (msg.sender != address(this) && to == address(this)) { // Sell transaction tax = ( _value * SELL_TAX_RATE) / 100; balanceOf[taxAddress] += tax ; } if (msg.sender == address(this)) { // Buy transaction tax = ( _value * BUY_TAX_RATE) / 100; balanceOf[taxAddress] += tax ; } uint256 tokensToTransfer = _value - tax; balanceOf[msg.sender] -= _value; balanceOf[to] += tokensToTransfer; emit Transfer(msg.sender, to, tokensToTransfer); if (tax >= 0) { emit Transfer(msg.sender, taxAddress, tax); } } function Approve(address spender, uint256 value) public { Allowancemsg.sender = value; emit Approval(msg.sender, spender, value); } function burn(uint256 value) external onlyOwner{ require(balanceOf[msg.sender] >= value, "Insufficient balance"); uint256 _value = value * (10 ** decimals); balanceOf[msg.sender] -= _value; totalSupply -= _value; emit Burn(msg.sender, _value); emit Transfer(msg.sender, address(0), _value); } function TransferOwnership(address _owner) public onlyOwner { emit TransferOwnerShip(Owner, _owner); Owner = _owner; } function RenounceOwner() public onlyOwner { emit TransferOwnerShip(Owner, address(0)); TransferOwnership(address(0)); } } '''
- Smart Contract
- Solidity
02Найкраща відповідь - Питання та відповіді експертівMay 27, 2023
Solidity and ethers.js Compute Different Addresses from the Same Signature
This script: const { ethers } = require('ethers'); async function recoverSigner(address, nonce, deadline, v, r, s) { const domain = { name: "RandomReachDebug5Local", version: "1", chainId: 31337, verifyingContract: "0x8464135c8F25Da09e49BC8782676a84730C318bC", }; const types = { RequestRandomNFT: [ { name: 'minter', type: 'address' }, { name: 'nonce', type: 'uint256' }, { name: 'deadline', type: 'uint256' }, ], }; const value = { minter: address, nonce: nonce, deadline: deadline, }; // Get the digest of the message const digest = ethers.utils._TypedDataEncoder.hash(domain, types, value); const sig = { r: r, s: s, v: v, }; if (sig.v But this solidity contract: // SPDX-License-Identifier: UNLICENSED pragma solidity ^0.8.18; import "@openzeppelin/contracts/token/ERC721/ERC721.sol"; import "@openzeppelin/contracts/utils/cryptography/draft-EIP712.sol"; contract GetAddressFromSig is ERC721, EIP712 { struct Request { address minter; uint256 nonce; uint256 deadline; } bytes32 public constant REQUEST_TYPEHASH = keccak256("Request(address minter,uint256 nonce,uint256 deadline)"); // Initialize _DOMAIN_SEPARATOR directly with static values bytes32 private immutable _DOMAIN_SEPARATOR = keccak256( abi.encode( keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"), keccak256(bytes("RandomReachDebug5Local")), // static name keccak256(bytes("1")), // static version 31337, // static chainId 0x8464135c8F25Da09e49BC8782676a84730C318bC // static verifyingContract ) ); constructor(string memory name, string memory symbol) ERC721(name, symbol) EIP712(name, "1") {} function domainSeparator() public view returns (bytes32) { return _DOMAIN_SEPARATOR; } function recoverSigner(Request memory request, uint8 v, bytes32 r, bytes32 s) public view returns (address) { bytes32 digest = keccak256( abi.encodePacked( "\x19\x01", _DOMAIN_SEPARATOR, keccak256( abi.encode( REQUEST_TYPEHASH, request.minter, request.nonce, request.deadline ) ) ) ); // ECDSA.recover returns the address that is associated with the public key // that was used to sign the given data, in this case, the digest. return ECDSA.recover(digest, v, r, s); } } Deployed with this script in hardhat: import { ethers } from "hardhat"; const hre = require("hardhat"); const dotenv = require("dotenv"); dotenv.config(); async function main() { const GetAddressFromSig = await hre.ethers.getContractFactory("GetAddressFromSig"); const gasPrice = await GetAddressFromSig.signer.getGasPrice(); console.log(Current gas price: ${gasPrice}); const estimatedGas = await GetAddressFromSig.signer.estimateGas( GetAddressFromSig.getDeployTransaction("RANDOM NFT 5", "RNFT5"), ); console.log(Estimated gas: ${estimatedGas}); const deploymentPrice = gasPrice.mul(estimatedGas); const deployerBalance = await GetAddressFromSig.signer.getBalance(); console.log(Deployer balance: ${ethers.utils.formatEther(deployerBalance)}); console.log(Deployment price: ${ethers.utils.formatEther(deploymentPrice)}); const getAddressFromSig = await GetAddressFromSig.deploy("RANDOM NFT 5", "RNFT5"); await getAddressFromSig.deployed(); console.log("GetAddressFromSig deployed to:", getAddressFromSig.address); } main() .then(() => process.exit(0)) .catch((error) => { console.error(error); process.exit(1); }); And ran with these commands in the hardhat console: const Token = await ethers.getContractFactory("GetAddressFromSig"); const token = await Token.attach("0x8464135c8F25Da09e49BC8782676a84730C318bC"); const request = { minter: "0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266", nonce: ethers.BigNumber.from("0"), deadline: ethers.BigNumber.from("1685162164") }; const v = 28 const r = "0xe0e4cc2f8b6bac3784f9feb3db4382291631d5f317d08a0b82305e5eb5ffc60a"; const s = "0x0416d521d12e26b8fc1f4bd566d5d67c5dffebe9564fe90db4f12c0a69b63d5e"; const signer = await token.recoverSigner(request, v, r, s); console.log(The signer is: ${signer}); Gives this output: The signer is: 0xeB7265f6625EaE66403a637c073E63ccf33b8Cdc So why does the javascript calculate 0x1AB26702A8068a247BD33a9555dfEf791d2BD68D, while hardhat's solidity compiler calculates 0xeB7265f6625EaE66403a637c073E63ccf33b8Cdc?
- Smart Contract
- Solidity
21Найкраща відповідь - Питання та відповіді експертівMay 26, 2023
Why does Solidity produce a different address from a private key than ether.js does?
I have this function in my solidity contract: function requestRandomNFT( address minter, uint256 nonce, uint256 deadline, uint8 v, bytes32 r, bytes32 s, uint256 randomUint256 ) external payable { require(block.timestamp { if (window.ethereum && randomReachDebug5Address) { console.log("initContract is running"); // If you use MetaMask // const provider = new ethers.providers.Web3Provider(window.ethereum); // If you use a local node (e.g., Ganache) const provider = new ethers.providers.JsonRpcProvider('http://localhost:8545'); const balance = await provider.getBalance(connectedAddrs); console.log("Balance: ", ethers.utils.formatEther(balance)); const contractInstance = new ethers.Contract(randomReachDebug5Address, RandomReachDebug5Local.abi, provider.getSigner()); console.log(contract is set here: ${contractInstance}); if (!sigData) { setContract(contractInstance); try { const nonce = await contractInstance.nonces(connectedAddrs); console.log("Nonce fetched: ", nonce); const deadline = Math.floor(Date.now() / 1000) + 120; // 2 minutes from now const sig = await signRandomNFTRequest(connectedAddrs, nonce, deadline); setSigData(sig); const randomUint256 = ethers.utils.hexlify(ethers.BigNumber.from(ethers.utils.randomBytes(32))); // generating random uint256 const argsInUseEffect = [connectedAddrs, nonce.toString(), deadline, sig.v, sig.r, sig.s, randomUint256]; console.log("Args in use effect: ", argsInUseEffect); setArgs(argsInUseEffect); } catch (error) { console.error("Error fetching nonce: ", error); setFetchNonceError(error); } } console.log(sig is here: ${sigData}); console.log(args is here: ${args}); } }, [args, connectedAddrs, randomReachDebug5Address, setContract]); useEffect(() => { initializeContract(); }, [initializeContract]); console.log(args outside of use effect ${args}); const { config, prepareError, isPrepareError } = usePrepareContractWrite({ address: randomReachDebug5Address, abi: RandomReachDebug5Local.abi, functionName: 'requestRandomNFT', args: args, value: '10000000000000000', // This is 0.01 Ether represented in Wei gas: 300000n, // Set your desired gas limit here gasPrice: parseGwei('50'), }); console.log(this is config: ${config}); const { data, error, isError, write } = useContractWrite(config || {}); console.log(this is the error ${error} and this is the error bool ${isError}); const { isLoading, isSuccess } = useWaitForTransaction({hash: data?.hash}); const mintNFT = () => { if (sigData) { console.log('Minting...'); write?.(); } else { console.error('sigData is not defined.'); } }; return { mintNFT, isLoading, isSuccess, isError, error, data, write, isPrepareError, prepareError, fetchNonceError }; } So here's the weird thing... When I ran the minting code within a next.js app, I got this in my console for the hardhat node: console.log: below this is signer 0x2d0b2215d4e00807a6982877a9762ef41541ecef below this is aithorizedAccount 0x1ab26702a8068a247bd33a9555dfef791d2bd68d But the private key I used gives me the address 0x1AB26702A8068a247BD33a9555dfEf791d2BD68D when I test it in javascript with ethers.js, but solidity gives me 0x2d0b2215d4e00807a6982877a9762ef41541ecef ??? I used this script with const privateKey = "0x REST OF MY PRIVATE KEY": const ethers = require('ethers'); function getAddressFromPrivateKey(privateKey) { const wallet = new ethers.Wallet(privateKey); return wallet.address; } const privateKey = "0x REST OF MY PRIVATE KEY"; console.log(getAddressFromPrivateKey(privateKey)); // This should log your expected address This code gives me 0x1AB26702A8068a247BD33a9555dfEf791d2BD68D, but my solidity code gives me 0x2d0b2215d4e00807a6982877a9762ef41541ecef. That doesn't make any sense. Why is this happening?
- Smart Contract
- Solidity
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Зароби свою частку з 1000 Sui
Заробляй бали репутації та отримуй винагороди за допомогу в розвитку спільноти Sui.
- Solidity
- Smart Contract
- Solidity Compiler
- Use cases
- Yul
- Optimizer
- Language Grammar
- Internals
- Private
- My ERC721 contract successfully deploys, but I can't verify the contract's source code with hardhat21
- Solidity and ethers.js Compute Different Addresses from the Same Signature21
- can't understand what are the locations(uint256)22
- How to reverse keccak256 in solidity22
- Clarification on Gas Refunds and Comparison Between "require" and "revert" in Smart Contracts21