Getting Block Hash of another contract - solidity

I've seen some problems with calling functions from other contracts but I believe my problem is fairly genuine to demand a separate question if only to be negated in its possibility.
So I am trying to call a contract within another contract. Is it possible to get the blockhash of a particular block number of the callee contract within my caller? If so how?
Every syntax I've attempted fails for some reason.
Contract A
enter code here
contract DiceGame {
uint256 public nonce = 0;
uint256 public prize = 0;
event Roll(address indexed player, uint256 roll);
event Winner(address winner, uint256 amount);
constructor() payable {
resetPrize();
}
function resetPrize() private {
prize = ((address(this).balance * 10) / 100);
}
function rollTheDice() public payable {
require(msg.value >= 0.002 ether, "Failed to send enough value");
bytes32 prevHash = blockhash(block.number - 1);
bytes32 hash = keccak256(abi.encodePacked(prevHash, address(this), nonce));
uint256 roll = uint256(hash) % 16;
console.log('\t'," Dice Game Roll:",roll);
nonce++;
prize += ((msg.value * 40) / 100);
emit Roll(msg.sender, roll);
if (roll > 2 ) {
return;
}
uint256 amount = prize;
(bool sent, ) = msg.sender.call{value: amount}("");
require(sent, "Failed to send Ether");
resetPrize();
emit Winner(msg.sender, amount);
}
receive() external payable { }
}
Contract B
enter code here
contract RiggedRoll is Ownable {
DiceGame public diceGame;
constructor(address payable diceGameAddress) {
diceGame = DiceGame(diceGameAddress);
}
//Add withdraw function to transfer ether from the rigged contract to an address
//Add riggedRoll() function to predict the randomness in the DiceGame contract and only roll when it's going to be a winner
function riggedRoll(bytes32 riggedHash) public payable {
riggedHash = address(diceGame).blockhash(block.number-1); //I am aware this syntax is broken but I am not able to find a legitimate one to access the data from contract A.
}
//Add receive() function so contract can receive Eth
receive() external payable { }
}

A contract doesn't know when it was last called, unless you explicitly store this information.
Then you can get the block hash using the native blockhash() function (accepts the block number as a parameter).
contract Target {
uint256 public lastCalledAtBlockNumber;
// The value is stored only if you invoke the function using a (read-write) transaction.
// If you invoke the function using a (read-only) call, then it's not stored.
function foo() external {
lastCalledAtBlockNumber = block.number;
}
}
bytes32 blockHash = blockhash(block.number);

Related

What is missing from this Smart Contract?

I am working on a smart contract, and my goal is that when a certain (variable) amount of eth gets send to the contract, it gets split and payed to three adresses. I currently have this code. Am I missing something? It doesn't work in Remix unfortunately. Thanks in advance for your valuable time!
`pragma solidity ^0.6.0;
contract PaymentSplitter {
address payable addressOne;
address payable addressTwo;
address payable addressThree;
uint256 amount;
constructor(address payable _addressOne = 0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2, address payable _addressTwo = 0x4B20993Bc481177ec7E8f571ceCaE8A9e22C02db, address payable _addressThree = 0x78731D3Ca6b7E34aC0F824c42a7cC18A495cabaB) public {
addressOne = _addressOne;
addressTwo = _addressTwo;
addressThree = _addressThree;
}
function splitPayment(uint256 _amount) public {
amount = _amount;
addressOne.transfer(_amount / 3);
addressTwo.transfer(_amount / 3);
addressThree.transfer(_amount / 3);
}
function getSplitAmount() public view returns (uint256) {
return amount;
}
// This will be invoked when the contract receives a payment
function() external payable {
splitPayment(msg.value);
}
}`
We tried various smart contract, but without any significant results
I modified your smart contract. I put some notes, to understand you some errors in your logic:
// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;
contract PaymentSplitter {
address payable addressOne;
address payable addressTwo;
address payable addressThree;
uint256 amount;
constructor(address _addressOne, address _addressTwo, address _addressThree) public {
addressOne = payable(_addressOne);
addressTwo = payable(_addressTwo);
addressThree = payable(_addressThree);
}
// NOTE: Avoid passing parameter with value because with this statement 'address(this).balance' I receive the entire amount of Ether stored in smart contract
function splitPayment() public {
// NOTE: I retrieve entire amount stored in smart contract balance after send value to it
uint smartContractBalance = address(this).balance;
// NOTE: Since smart contract balance should be divided into three equal part the amount, I make this operation one time and put the value inside 'amount' variable. Then
// I transfer the equal amount to three accounts.
amount = smartContractBalance / 3;
addressOne.transfer(amount);
addressTwo.transfer(amount);
addressThree.transfer(amount);
}
function getSplitAmount() public view returns (uint256) {
return amount;
}
// This will be invoked when the contract receives a payment
receive() external payable {
splitPayment();
}
}
NOTE: Consider to use address.call{value}() for send amount from smart contract to accounts.
Is this a better contract? A few changes, and different amounts have to be sent to different addresses.
pragma solidity ^0.8.17;
contract Blockbook{
address payable public address1;
address payable public address2;
address payable public address3;
constructor(address payable _address1, address payable _address2, address payable _address3) public {
address1 = _address1;
address2 = _address2;
address3 = _address3;
}
function splitPayment(uint amount) public payable {
address1.transfer(amount * 0.8);
address2.transfer(amount * 0.1);
address3.transfer(amount * 0.1);
}
receive() external payable {
splitPayment(msg.value);
}
function updateAddresses(address payable _address1, address payable _address2, address payable _address3) public {
address1 = _address1;
address2 = _address2;
address3 = _address3;
}
}

Problem sending eth from contract to contract

pragma solidity ^0.8.7;
// SPDX-License-Identifier: MIT
contract Client {
address payable private hub;
address payable public owner;
uint256 public balance;
constructor(address payable _hub) {
hub = _hub;
owner = payable(msg.sender);
}
receive() payable external {
balance += msg.value;
}
function withdraw(address payable destAddr) public {
require(msg.sender == owner, "Only owner can withdraw funds");
uint amount = address(this).balance;
destAddr.transfer(amount);
}
function start() public payable {
require(msg.sender == owner, "Only owner can start the process");
uint amount = address(this).balance;
hub.transfer(amount);
balance = 0;
}
function setHub(address payable _new) public {
require(msg.sender == owner, "Only owner can change address");
hub = _new;
}
}
Hi i have a problem, when I deploy this contract and put as input (hub) the other contract, then send eth to this contract, i call the "start" function and throw a gas estimation error.
Someone who can help me pls...
I'm expecting that calling the start function fund will be sent to the other contract that also have a function for receiving eth
receive() payable external {
balance += msg.value;
}
You are getting that gas estimation error because your receive function on the second contract is not empty and the transaction does not have enough gas to execute the code. transfer only sends the amount of gas necessary to execute a transfer of ether (21,000 gas) and nothing more.
You can use call instead of transfer to send ether and set the amount of gas that you want to send. transfer is actually no longer recommended for sending ether.

A Lottery Solidity Smart Contract Accept token as payment instead of ether

pragma solidity ^0.4.21;
contract Lottery {
address public manager;
address[] public players;
constructor() public {
manager = msg.sender;
}
function enter() public payable {
require(msg.value > .01 ether);
players.push(msg.sender);
}
function random() private view returns (uint) {
return uint(keccak256(abi.encodePacked(block.difficulty, now, players)));
}
function pickWinner() public restricted {
uint index = random() % players.length;
players[index].transfer(address(this).balance);
players = new address[](0);
}
function getPlayers() public view returns (address[]) {
return players;
}
modifier restricted() {
require(msg.sender == manager);
_;
}
}
I want o change the function
function enter() public payable {
require(msg.value > .01 ether);
players.push(msg.sender);
}
Instead of ether, user use our token/erc20 to enter the lottery
You can define an interface (in your contract) of the token contract. Since you're only going to be using the transferFrom() function, this is the only function that you need to define in the interface (no matter that the token contract contains other functions as well).
interface IERC20 {
function transferFrom(address _from, address _to, uint256 _amount) external returns (bool);
}
The you can execute the transferFrom() function of the token, passing it arguments:
from: the user executing your enter() function
to: your contract
amount: Assuming the token has 18 decimals (most tokens do), you can use the ether helper unit, because it effectively calculates "0.01 * 10^18 (or 10^16, or 10000000000000000) of the token smallest units", which is 0.01 of the token. Otherwise, you'll need to recalculate this number based on the token decimals.
function enter() public payable {
IERC20 token = IERC20(address(0x123)); // Insert the token contract address instead of `0x123`
require(token.transferFrom(msg.sender, address(this), .01 ether));
players.push(msg.sender);
}
Important: Mind that the user needs to approve() your contract to spend their tokens beforehand (from their address), otherwise the token transfer would fail. There's a security reason for that, read more about it in the bottom part of this answer.

How to make an API call in solidity?

I have a smart contract that I’m trying to make, it pays out the winners of my League of Legends tournament. However I’m running into an issue. I need to make an API call to get the winner of the match, I have a simple URL that I’ve make.
"example-winner.com/winner"
And it returns simple JSON with the address of the winner:
{"winner":"0xa7D0......."}
However, I’m not sure how to make the API call to the outside function. I know I need to use some sort of oracle technology.
Any thoughts? Below is my code:
pragma solidity ^0.4.24;
contract LeagueWinners{
address public manager;
address[] public players;
uint256 MINIMUM = 1000000000000000;
constructor() public{
manager = msg.sender;
}
function enter() public payable{
assert(msg.value > MINIMUM);
players.push(msg.sender);
}
function getWinner() public{
assert(msg.sender == manager);
// TODO
// Get the winner from the API call
result = 0; // the result of the API call
players[result].transfer(address(this).balance);
// returns an adress object
// all units of transfer are in wei
players = new address[](0);
// this empties the dynamic array
}
}
You can use Chainlink as your Oracle.
As many have mentioned, you will need an oracle to get your API call. Something that is important to note, your contract is actually asking an oracle to make your API call for you, and not making the API call itself. This is because the blockchain is deterministic. For more information see this thread.
To answer your question, you can use the decentralized oracle service Chainlink.
You'd add a function:
function getWinner()
public
onlyOwner
{
Chainlink.Request memory req = buildChainlinkRequest(JOB, address(this), this.fulfill.selector);
req.add("get", "example-winner.com/winner");
req.add("path", "winner");
sendChainlinkRequestTo(ORACLE, req, ORACLE_PAYMENT);
}
For the purpose of the following exmaple, we are going to pretend you want to return a uint256 instead of an address. You can return a bytes32 and then convert it to an address, but for simplicity let's say the API returns the index of the winner. You'll have to find a node and jobId that can make a http.get request and return a uint256 object. You can find nodes and jobs from market.link. Each testnet (Ropsten, Mainnet, Kovan, etc) has different node addresses, so make sure you pick the right ones.
For this demo, we are going to use LinkPool's ropsten node
address ORACLE=0x83F00b902cbf06E316C95F51cbEeD9D2572a349a;
bytes32 JOB= "c179a8180e034cf5a341488406c32827";
Ideally, you'd choose a number of nodes to run your job, to make it trustless and decentralized. You can read here for more information on precoordinators and aggregating data. disclosure I am the author of that blog
Your full contract would look like:
pragma solidity ^0.6.0;
import "github.com/smartcontractkit/chainlink/evm-contracts/src/v0.6/ChainlinkClient.sol";
contract GetData is ChainlinkClient {
uint256 indexOfWinner;
address public manager;
address payable[] public players;
uint256 MINIMUM = 1000000000000000;
// The address of an oracle
address ORACLE=0x83F00b902cbf06E316C95F51cbEeD9D2572a349a;
//bytes32 JOB= "93fedd3377a54d8dac6b4ceadd78ac34";
bytes32 JOB= "c179a8180e034cf5a341488406c32827";
uint256 ORACLE_PAYMENT = 1 * LINK;
constructor() public {
setPublicChainlinkToken();
manager = msg.sender;
}
function getWinnerAddress()
public
onlyOwner
{
Chainlink.Request memory req = buildChainlinkRequest(JOB, address(this), this.fulfill.selector);
req.add("get", "example-winner.com/winner");
req.add("path", "winner");
sendChainlinkRequestTo(ORACLE, req, ORACLE_PAYMENT);
}
// When the URL finishes, the response is routed to this function
function fulfill(bytes32 _requestId, uint256 _index)
public
recordChainlinkFulfillment(_requestId)
{
indexOfWinner = _index;
assert(msg.sender == manager);
players[indexOfWinner].transfer(address(this).balance);
players = new address payable[](0);
}
function enter() public payable{
assert(msg.value > MINIMUM);
players.push(msg.sender);
}
modifier onlyOwner() {
require(msg.sender == manager);
_;
}
// Allows the owner to withdraw their LINK on this contract
function withdrawLink() external onlyOwner() {
LinkTokenInterface _link = LinkTokenInterface(chainlinkTokenAddress());
require(_link.transfer(msg.sender, _link.balanceOf(address(this))), "Unable to transfer");
}
}
This would do about everything you need.
If you can't adjust the API to return a uint, you can return a bytes32 and then convert it to an address or a string.
function bytes32ToStr(bytes32 _bytes32) public pure returns (string memory) {
bytes memory bytesArray = new bytes(32);
for (uint256 i; i < 32; i++) {
bytesArray[i] = _bytes32[i];
}
return string(bytesArray);
}
You cannot. The vm does not have any I/O outside of the blockchain itself. Instead you will need to tell your smart contract who the winner is and then the smart contract can just read the value of that variable.
This design pattern is also known as the "oracle". Google "Ethereum oracle" for more info.
Basically your web server can call your smart contract. Your smart contract cannot call your web server. If you need your smart contract to access a 3rd party service then your web server will need to make the request then forward the result to solidity by calling a function in your smart contract.
You didn't properly explain what you are trying to do. Are you having trouble with the solidity code? or rather with your server? Here is an edited version. See if it helps.
pragma solidity ^0.4.24;
contract LeagueWinners{
address public manager;
//address[] public players;
uint256 MINIMUM = 1000000000000000;
constructor() public{
manager = msg.sender;
}
struct Player {
address playerAddress;
uint score;
}
Player[] public players;
// i prefer passing arguments this way
function enter(uint value) public payable{
assert(msg.value > MINIMUM);
players.push(Player(msg.sender, value));
}
//call this to get the address of winner
function winningPlayer() public view
returns (address winner)
{
uint winningScore = 0;
for (uint p = 0; p < players.length; p++) {
if (players[p].score > winningScore) {
winningScore = players[p].score;
winner = players[p].playerAddress;
}
}
}
// call this to transfer fund
function getWinner() public{
require(msg.sender == manager, "Only a manager is allowed to perform this operation");
// TODO
address winner = winningPlayer();
// Get the winner from the API call
//uint result = 0; // the result of the API call
winner.transfer(address(this).balance);
// returns an adress object
// all units of transfer are in wei
delete players;
// this empties the dynamic array
}
}
At least that is what I understand by your question.

Why Sender address emitted in event differs from saved in storage?

The wallet address that is sent through event differs from the one stored in contract
Hi, I have a contract that is deployed to development network through truffle.
I trigger function that looks like this:
struct Round {
bool isValue;
uint32 id;
RoundState state;
address[] addresses;
RoundBet[] bets;
mapping(address => bool) betUsers;
mapping(address => uint256) userBets;
uint256 winTicket;
uint256 amount;
uint256 lastTicket;
address winner;
}
.....
event roundBet(
address user,
uint256 amount,
uint256 start,
uint256 end
);
......
function test() payable public {
Round storage round = roundsHistory[currentRound];
require(round.isValue == true);
require(round.state == RoundState.started);
require(msg.value >= MIN_BET);
uint256 amount = msg.value - msg.value % MIN_STEP;
if(!round.betUsers[msg.sender]){
round.addresses.push(msg.sender);
round.betUsers[msg.sender] = true;
}
round.userBets[msg.sender] += amount;
uint256 sticket = round.lastTicket + 1;
uint256 eticket = sticket + amount;
uint256 length = round.bets.push(RoundBet(true, sticket, eticket, msg.sender, amount));
round.amount += amount;
round.lastTicket = eticket;
if(round.addresses.length == 2){
round.state = RoundState.running;
emit roundTimerStart(currentRound);
}
emit roundBet(msg.sender,amount, sticket, eticket);
}
AS you can see I emit roundBet event at the end of function call. The problem is that value of "user" of that event differs from msg.sender that is stored in round.addresses(values stored in round.addresses - is currect and the one emited - is wrong)
If you are using Metamask, keep in mind that it does not switch the account set as msg.sender to the contract, it seems to use the first account (0) to sign every transaction.
We encountered the same problem during a school project.
First of all about platform. It was tron not ethereum. May be in ethereum there is no such issue.
So what I did:
I do not pass address in event. I save it in internal structure
In event I do pass index of saved address in structure
I've wrote a separate method that returns address (and other usefull info) from internal structures by its index.
So by using this workaround I was able to get needed information from contract.