Assuming I have a wallet, I want to authorize another wallet to send a transfer on my behalf, how do I implement the above using the following practice.
pragma solidity ^0.8.0;
import 'Token.sol';
contract TransferToken{
function transferFrom(address recipient, uint amount) external {
Token token = Token(0xd9145CCE52D386f254917e481eB44e9943F3555);
token.transferFrom(msg.sender, recipient, amount);
}
}
contract Owner {
function transfer(address recipient, uint amount) external {
Token token = Token(0xd9145CCE52D386f254917e481eB44e9943F39138);
token.approve(0x617F2E2fD72FD9D5503197092aC168c91465E7f2, amount);
TransferToken transferToken = TransferToken(0x617F2E2fD72FD9D5503197092aC168c91465E7f2);
transferToken.transferFrom(recipient, amount);}}
in the above example, i am using the openZappelin implementation for ERC20 on the import (Token.sol)
now my question is this ... since I want to use a real wallet with ERC20 token how do I implement the above example, I am thinking for this I don't need the import anymore, but I don't know how to implement it without too many mistakes already, I very new to solidity and I am using remix for the above implementation
will be glad if i could get a help on this
Related
I want to transfer some ether form my address to the smart contract, I have tried the code below but it doesn't work. How to transfer ether through msg.sender?
pragma solidity >=0.7.0 <0.9.0;
contract Test {
function testTransfer() external payable {
bool sent = payable(address(this)).send(msg.value);
require(sent, "invalid balance");
}
}
Once I trigger the function with the value of 1 ether, the error output is as below:
I'm sure that I have enough Ether in my address. What should I do to transfer the Ether? Thanks!
The transaction fails because the smart contract is trying to transfer the ether to himself, and the smart contract doesn't have defined the receive function so it can receive ether that way, for your example you could simply remove all the code inside the function and make another function to check the contract balance and it will work
pragma solidity >=0.7.0 <0.9.0;
contract Test {
function testTransfer() external payable {}
function getBalance() external view returns (uint256) {
return address(this).balance;
}
}
I Need to Write a Smart Contract, In This Smart Contract User Can Send Token to Each Account in ERC-20 Network.
sender :0x5C2879Ec550e2F65D557b540B7DEAB3A6d478d62
recipient : 0xB643992c9fBcb1Cb06b6C9eb278b2ac35e6a2711
token Address : 0xa36085F69e2889c224210F603D836748e7dC0088
Kovan Testnet
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol";
contract DexB is ERC20("KiaDex","DEX") {
function SendTokenFromAddress(address token,address sender,address recipient,uint256 amount)
external {
IERC20 token = IERC20(token);
token.allowance(sender,address(token));
token.approve(sender,amount);
require(token.balanceOf(sender) >=amount , "your balance is low" ) ;
token.transferFrom(sender,recipient, amount);
}
}
when i want to send token from this address 0x5C2879Ec550e2F65D557b540B7DEAB3A6d478d62 to this address 0xB643992c9fBcb1Cb06b6C9eb278b2ac35e6a2711 it dose not work and show me this message and afte that show not success transaction :
**whats the problem ? how can i sene Token from User Address to User Address in solidity ? **
The sender, which in your case is 0x5C2879Ec550e2F65D557b540B7DEAB3A6d478d62 needs to approve the wallet address that's calling the sendTokenFromAddress function. The contract cannot do that on behalf of the account that needs to send tokens.
I'm trying to transfer an ERC721 token, but I'm getting the error ERC721: transfer caller is not owner nor approved for the transferToken method.
Main.sol
import "./ERC721.sol";
import "./Counters.sol";
contract Main is ERC721 {
using Counters for Counters.Counter;
Counters.Counter internal _tokenIds;
address payable internal admin;
constructor() ERC721("MyToken", "TOKEN") {
admin = payable(msg.sender);
}
}
Auction.sol
import "./Main.sol";
contract Auction is Main {
struct AuctionInfo {
uint256 tokenId;
address highestBidder;
uint highestBid;
}
mapping(string => AuctionInfo) private _auctionInfo;
function createAuction(string memory id) public {
_tokenIds.increment();
uint256 newTokenId = _tokenIds.current();
_mint(msg.sender, newTokenId);
_auctionInfo[id].tokenId = newTokenId;
}
function transferToken(string memory id) public {
require(msg.sender == _auctionInfo[id].highestBidder, "You are not the highest bidder");
safeTransferFrom(address(this), _auctionInfo[id].highestBidder, _auctionInfo[id].tokenId);
}
// other methods...
}
The minting contract is this and the owner of the token is the msg.sender of the minting method if I'm not mistaken. Am I to use the approve (or setApprovalForAll) for this each time before transferring? I've tried this, payable(this), and address(this) for the safeTransferFrom method, but none seem to be working.
For example, I tried the following, but get the same revert message:
approve(address(this), _auctionInfo[id].tokenId);
this.safeTransferFrom(address(this), _auctionInfo[id].highestBidder, _auctionInfo[id].tokenId);
The main principle behind any Blockchain is that nobody on the blockchain network should be trusted, and still the transactions should happen fool proof, with no possibility of any cheating being done (barring of course of some hacking).
If you invoke the approve method from the Auction contract, then the msg.sender for the approve function in the ERC721 token contract is your auction contract address. So, in other words, your Auction Contract is trying to approve itself to sell someone else's NFTs, which is not very trustworthy.
What should really happen is that owner of the NFT should invoke the approve method of the ERC721 contract - i.e. the transaction that you send for the approve function call, should be signed by the NFT owner wallet address. This way, the msg.sender for the approve function in the ERC721 contract will be the owner of the NFT. As per the ERC721 standards, the owner of the NFT can approve anyone they want, to sell their NFT(s), as the no-trust in the network is still maintained (At least I should be able to trust myself). The approve method should be invoked from within your DAPP, before the transferToken function is invoked from the DAPP.
Hope that explains why you are unable to transfer your ERC721 tokens.
Because of the internal visibility of the ERC721._approve() function, you can effectively perform the approval for the user.
Then you'll be able to execute the safeTransferFrom(tokenOwner, receiver, tokenId) from your contract, because your contract address is approved to operate this specific token even though it belongs to the tokenOwner.
This snippet mints the token, assigning the ownership to the msg.sender. But then it also calls the _approve() function that doesn't contain any validations and simply assigns the approval of the token to the Auction address.
pragma solidity ^0.8;
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC721/ERC721.sol";
contract Auction is ERC721 {
constructor() ERC721("CollectionName", "Symbol") {}
function createAuction() public {
uint256 newTokenId = 1;
_mint(msg.sender, newTokenId);
_approve(address(this), newTokenId);
}
}
You can see from the screenshot that the owner is 0x5B... (the user address) and that the token is approved for 0xd9... (the contract address).
Note: The _approve() function is internal - it can be called from the ERC721 contract and contracts deriving from it (in your case Main and Auction), but it can't be called from external contracts or end user addresses.
First I pre-install a contract A(address(A)). Then I install a contract B (address(B)) to invoke A by using call interface. Lastly I invoke the contract by using his address(x). I meant to use the address(x) to invoke A, but actually the address(B) invoke A. So how can I use address(x) to invoke A?"
pragma solidity ^0.4.21;
contract TransferERC20 {
event TransferEvent (
bool _flag,
string _invoiceId,
address _erc20ContractHash,
address indexed _from,
address indexed _to,
uint256 _value
);
function transfer(string _invoiceId, address _erc20ContractHash,address _from, address _to, uint256 _amount) public returns (bool) {
bytes4 methodTransfer = bytes4(keccak256("transfer(address,uint256)"));
if(_erc20ContractHash.call(methodTransfer, _to, _amount)) {
emit TransferEvent(true, _invoiceId, _erc20ContractHash, _from, _to, _amount);
return true;
}
emit TransferEvent(false, _invoiceId, _erc20ContractHash, _from, _to, _amount);
return false;
}
}
The above code intends to call ERC20 contract which is pre-installed on ethereum testnet. However I invoke failed because the address is changed to the the TransferERC20 address. How can I realize the transfer function by using the TransferERC20 callor's address. THKS.
The token holder first needs to set an allowance using approve on the ERC20 token for the TransferERC20 contract and only then can they call transfer on the TransferERC20 contract which should call transferFrom on the ERC20 token.
This requires two transactions, one for approve and one for transferFrom.
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
Alternatively you could look at creating ERC777 tokens (no need to do approve and transferFrom in two separate transactions). See the documentation for details: https://docs.openzeppelin.com/contracts/2.x/tokens#ERC777
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
I am very new using Solidity to create Ethereum contracts and would like to know if the contract I have created is first correct and safe to use.
What I am doing in this contract is allowing the user to send some ETH from their wallet to a friends wallet but also take a $0.05 fee (194740000000000 wei at time of writing) for using my services.
Now when testing the contract using remix all works fine, but as I am new to solidity contracts I just wanted to get some expert opinions to make sure I am doing everything correctly and safety.
My contract code is:
pragma solidity ^0.5.1;
contract Forwarder {
address payable public receiversAddress = 0x14723A09ACff6D2A60DcdF7aA4AFf308FDDC160C;
address payable public feeAddress = 0xdD870fA1b7C4700F2BD7f44238821C26f7392148;
constructor() payable public {
uint amountToSendReceiver = msg.value-194740000000000;
receiversAddress.transfer(amountToSendReceiver);
feeAddress.transfer(194740000000000);
}
}
As mentioned everything works fine in remix, but is my contract code correct and safe to use? There is no way to use the contract after to maybe steal funds or have any vulnerabilities?
Yes, your code is pretty safe. The only thing I would like to add is line with require condition for code maintainability
And if your vars are not changeable, its better to use constant to make your contract cheaper for deploy ;)
Functions can be declared constant in which case they promise not to
modify the state.
pragma solidity ^0.5.1;
contract Forwarder {
address payable public constant receiversAddress = 0x14723A09ACff6D2A60DcdF7aA4AFf308FDDC160C;
address payable public constant feeAddress = 0xdD870fA1b7C4700F2BD7f44238821C26f7392148;
uint256 constant feeAmount = 194740000000000;
constructor() payable public {
require(msg.value >= feeAmount); // for maintainability, your tx will be reverted anyway, just to show why
feeAddress.transfer(feeAmount); // transfer fee
receiversAddress.transfer(address(this).balance); // transfer remaining amount of msg.value
}
}