I found such way, when one general interface with structure is created and then contract A and B inherit the interface with structure.
But I'm wondering if there are other ways?
And could there be a case where a contract with a structure can be updated?
pragma experimental ABIEncoderV2;
pragma solidity ^0.6.0;
interface params {
struct structTest {
uint256 data;
}
}
contract contractA is params{
function testCall(structTest calldata _structParams) public pure returns (uint256){
return _structParams.data;
}
}
contract contractB is params{
contractA aContractInstance;
constructor (address _a) public {
aContractInstance = contractA(_a);
}
function test(structTest calldata _structParams) public view returns(uint256){
// call contract A from B and pass structure
return aContractInstance.testCall(_structParams);
}
}
interface IContractA {
struct User {
address addr;
}
function getUser(aaddress addr) external view returns (User memory user);
}
contract contractB{
function getUserFromContractA(address addr) public view
returns (IContractA.User memory user)
{
ContractA = IContractA(addrContractA);
user = ContractA.getUser(addr);
}
}
Related
I am using the OpenZeppelin's ERC721 Library, is there was a way to get the count of the number of times a token has been minted.
Is there a built-in mapping or function to check that?
You can use the Enumerable extension. The totalSupply() function returns the currently existing amount of tokens (minted minus burned), which in some cases might not the same thing as the total amount of minted tokens.
pragma solidity ^0.8;
import "#openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
import "#openzeppelin/contracts/token/ERC721/extensions/ERC721Burnable.sol";
/*
* `totalSupply()` (defined in ERC721Enumerable) returns 1
* even though 2 tokens were minted, but 1 was also burned
*/
contract MyCollection is ERC721Enumerable, ERC721Burnable {
constructor() ERC721("CollectionName", "Symbol") {
_mint(msg.sender, 1);
_burn(1);
_mint(msg.sender, 2);
}
// multiple parents define the same function
// overriding here just to point at the expected parent class
// related to the combination of `Burnable` and `Enumerable` in the same contract - not to `Enumerable` alone
function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal override(ERC721, ERC721Enumerable) {
return ERC721Enumerable._beforeTokenTransfer(from, to, tokenId);
}
// same reason for overriding as above
function supportsInterface(bytes4 interfaceId) public view override(ERC721, ERC721Enumerable) returns (bool) {
return ERC721Enumerable.supportsInterface(interfaceId);
}
}
Or you can override the _beforeTokenTransfer() hook and create a custom counter that takes into account only minting and ignores burning.
pragma solidity ^0.8;
import "#openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
import "#openzeppelin/contracts/token/ERC721/extensions/ERC721Burnable.sol";
/*
* `mintCounter` returns 2, ignores the burned tokens
*/
contract MyCollection is ERC721Enumerable, ERC721Burnable {
uint256 public mintCounter;
constructor() ERC721("CollectionName", "Symbol") {
_mint(msg.sender, 1);
_burn(1);
_mint(msg.sender, 2);
}
function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal override(ERC721, ERC721Enumerable) {
if (from == address(0)) {
mintCounter++;
}
return ERC721Enumerable._beforeTokenTransfer(from, to, tokenId);
}
function supportsInterface(bytes4 interfaceId) public view override(ERC721, ERC721Enumerable) returns (bool) {
return ERC721Enumerable.supportsInterface(interfaceId);
}
}
I need help how to fix the "else if" = only owner is allowed to call the _action from the main contract. this is just the logger. below is the contract logger.
contract logger {
function log(address _caller, uint _amount, string memory _action) public {
if (equal(_action, "withdraw")) {
revert("It's a frank!");
else if (equal(_caller, "owner"));
assert();
}
}
function equal(string memory _a, string memory _b) public pure returns (bool) {
return keccak256(abi.encode(_a)) == keccak256(abi.encode(_b));
So I am guessing you want to call the function from the main contract in the logger contract. So we need to know the address of the main contract and the function signature of the action function in the main contract. Suppose the function signature of action function in the main contract is action(unit256). And let's initialize the main contract in the constructor.
So the contract logger would look like this:
// SPDX-License-Identifier: MIT
pragma solidity 0.8.15;
import "./MainContract.sol";
contract Logger {
address private owner;
MainContract mainContract;
constructor(address _mainContract){
owner = msg.sender;
mainContract = new MainContract(_mainContract);
}
function log(address _caller, uint _amount, string memory _action, uint256 value) public {
if (equal(_action, "withdraw")) {
// Do whatever you want
}
else if (_caller == owner){
mainContract.action(value);
// Do whatever you want
}
}
function equal(string memory _a, string memory _b) public pure returns (bool) {
return keccak256(abi.encode(_a)) == keccak256(abi.encode(_b));
}
}
I am trying the below code, elementary reentrancy example.
The current code works but transfer or send doesn't work. It reverts. What are the reasons?
Note: I chose setCaller to reenter to test the fact that updating the dirty state variable (already modified var in the same tx) takes less gas.
// SPDX-License-Identifier: Unlicensed
pragma solidity 0.8.7;
contract TestFund {
// success, if caller is itself.
address public caller;
constructor() payable {}
function getBalance() public view returns (uint) {
return address(this).balance;
}
function emptyFn(address dummy) public {}
function setCaller(address _caller) public {
caller = _caller;
}
function withdraw() external {
caller = msg.sender;
// require(payable(msg.sender).send(1 wei));
// payable(msg.sender).transfer(1 wei);
(bool success, bytes memory data) = payable(msg.sender).call{gas: 2300, value:1 wei}("");
require(success);
}
}
contract Attack {
function getBalance() public view returns (uint) {
return address(this).balance;
}
function attack(address target) external {
TestFund(target).withdraw();
}
receive() external payable {
if (getBalance() == 1 wei) {
TestFund(msg.sender).setCaller(msg.sender);
}
}
}
In the following claimPayment function that is used to claim a payment made earlier to this contract, the line bytes32 message = prefixed(keccak256(abi.encodePacked(msg.sender, amount, nonce, this))); has this as part of the signed message. This makes me wonder what is this and what the type of this is. If I'm returning this in a function, what type is used for it? Thanks.
function claimPayment(uint256 amount, uint256 nonce, bytes memory signature) public {
require(!usedNonces[nonce]);
usedNonces[nonce] = true;
// this recreates the message that was signed on the client
bytes32 message = prefixed(keccak256(abi.encodePacked(msg.sender, amount, nonce, this)));
require(recoverSigner(message, signature) == owner);
payable(msg.sender).transfer(amount);
}
this is a pointer to the current class instance, as in many other programming languages. You can for example point to public methods:
pragma solidity ^0.8.0;
contract MyContract {
function foo() external {
this.bar();
}
function bar() public {
}
}
When this is typecasted, it takes a form of the address, where the current instance is deployed.
pragma solidity ^0.8.0;
contract MyContract {
function foo() external view returns (bytes memory) {
return abi.encodePacked(this);
}
function bar() external view returns (address) {
return address(this);
}
}
In order to calling a function 'isContract', with the parameter 'to' being an address, are valid both ways? :
to.isContract()
isContract(to)
Does Solidity allow both ways?
I have found both in different codes, and I don't know if just 'isContract(to)' is the right one, or if 'to.isContract()' means another different thing.
Thanks a lot for your help.
They're not the same.
to.isContract() suggests that you have defined an interface (in your code) that defines a isContract() function, and that the contract deployed at the to address implements this interface.
pragma solidity ^0.8.0;
interface ExternalContract {
function isContract() external returns (bool);
}
contract MyContract {
function foo() external {
ExternalContract to = ExternalContract(address(0x123));
bool returnedValue = to.isContract(); // calling `to`'s function `isContract()`
}
}
isContract(to) calls an external or internal function in your contract.
pragma solidity ^0.8.0;
contract MyContract {
function foo() external {
address to = address(0x123);
bool returnedValue = isContract(to); // calling your function `isContract()`
}
function isContract(address to) internal returns (bool) {
return true;
}
}
Edit: I forgot about one more case - using a library containing the isContract() function for an address. Example OpenZeppelin implementation: definition, usage.
library AddressLibrary {
function isContract (address _address) {
return true;
}
}
contract MyContract {
using AddressLibrary for address;
function foo() external {
address to = address(0x123);
bool returnedValue to.isContract(); // calling your function `isContract(to)`
}