I'm trying to transfer ether from an Account 1 to an Account 2. This is the code:
function pay(address _from, uint256 _tokenId) external payable noReentrant {
uint256 balance = msg.sender.balance;
require(balance > 0.011 ether, "There is not enough eth");
payable(__ADDRESS2__).transfer(0.001 ether);
}
receive() external payable {
}
fallback() external payable {
}
So here the msg.sender is Account 1 and this account wants to transfer eth to Account 2. Both accounts have ethers but it's throwing this error:
Error: Transaction reverted: function call failed to execute
I'm using hardhat to test this function. So I have a couple of doubts:
Is this the correct way to transfer tokens from Account 1 to 2? And here I'm not talking about transfering eth from Account 1 to address of the contract.
If it is, then, what's wrong with it?
First of all, the code you presented trasnfers ether from the contract to ADDRESS2, so the transaction probably reverts because the contract doesn't have enough ether. You should've checked that the caller sends you enough ether to transfer, i.e require(msg.value >= 0.001 ether).
Concerning the last two questions:
No, this code illustrates ether transfers. If you want to transfer ERC20 tokens, the OZ library would be a good start.
The reason it reverts is explained above. Sending ether is very different from sending ERC20 (or any other) tokens, consider checking the OpenZeppelin library.
Related
I am a newbie in the blockchain technology and I have question.
I just deployed an Ethereum smart contract to the Rinkeby testnet network and minted a few NFTs. When checking my contract address on rinkeby.etherscan.io I can see the smart contract's balance.
The question is, how can I transfer these ethereum in the smart contract balance to my wallet. Since I am the owner I should receive these ETH somehow to my metamask wallet no?
Smart contract includes the following function
// This will transfer the remaining contract balance to the owner.
// Do not remove this otherwise you will not be able to withdraw the funds.
(bool os, ) = payable(owner()).call{value: address(this).balance}('');
require(os);
}```
so it should be possible...
To be able to withdraw the funds from your contract to a wallet you own you must implement a withdraw method like so:
address public primary_wallet = YOUR_WALLET_ADDRESS
function withdraw() public payable onlyOwner {
(bool os,)= payable(primary_wallet).call{value:address(this).balance}("");
require(os);
}
You will also need to make sure that you import import "#openzeppelin/contracts/access/Ownable.sol"; to use the onlyOwner modifier. This allows only the person who deployed the contract to withdraw the funds and nobody else. This is a must. Hope this helps.
Per your current implementation, you need to manually invoke the withdraw() function from the owner address each time you want to withdraw ETH from the contract.
Your mint functions accept ETH and keep it on the contract address.
If you want to transfer the funds to the owner each time a mint is performed, you need to explicitly invoke the transfer from each of the mint functions. Example:
function mint(uint256 _mintAmount) public payable mintCompliance(_mintAmount) mintPriceCompliance(_mintAmount) {
require(!paused, 'The contract is paused!');
_safeMint(_msgSender(), _mintAmount);
// auto transfer received funds to the owner
payable(owner()).transfer(msg.value);
}
I am following a tutorial for a crowdfunding smart contract that accepts a token from users.
I have developed a simple ERC20 token, then I deploy the crowdfunding smart contract giving the address of the ERC20 token as the token accepted from users.
I would like to use the same smart contract with ethers. In other words, I would like people to fund the smart contract with ethers (using ganache and remix, my 10 users have 100 ethers each). Therefore, I need to deploy the smart contract giving the ethereum token address. What is the ether's address?
I am working with remix and ganache under web3 provider.
The native token of any EVM network (in your case Ether) does not have any address.
In Solidity, you can:
Accept ETH with the payable function modifier
Validate the amount sent by the user stored in the msg.value global property. The variable is read-only, the sender chooses how much they send and your contract can only validate that.
Send ETH with the native .transfer() function of address payable (extension of address) type. Do not confuse with the ERC20 custom transfer() function - these are two separate functions even though they have the same name.
pragma solidity ^0.8;
contract MyContract {
address owner = address(0x123);
// `payable` modifier allows the function to accept ETH
function foo() external payable {
// validate that the received amount is 1e18 wei (1 ETH)
require(msg.value == 1e18);
// typecast `address` variable (name `owner`)
// to `address payable` and effectively redirect the received value
// with the native `transfer()` function of the `address payable` type
payable(owner).transfer(msg.value);
}
}
If you need to work with approvals and other ERC-20 features, many contracts use WETH (Wrapped Ether) token that uses tokenomics supposed to maintain the same WETH price as ETH has, instead of using the regular ETH. Its production address depends on the network where its deployed. For example:
Ethereum: 0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2
Polygon: 0x7ceb23fd6bc0add59e62ac25578270cff1b9f619
I want to create a smart contract which people can transfer tokens without ether in their wallet.
Suppose A want to transfer ERC20 tokens to B, but he does not have ether in his wallet.
Does third party C can send the transaction for A and therefore pay the gas? Is it possible to create a function in the contract for this usgae?
I have searched online for a soloution and could not find one.
This is a key issue of Ethereum dApp development, but also of tokens. Here is a very old thread on Ethereum Stack Exchange, and also this one.
There are 2 options with their pros and cons:
Use signatures
Every function in your smart contract must have signature parameter.
People who want to interact with the smart contract must sign the function parameters with their account's private key and send it to the smart contract owner (via any communication channel).
The owner then submits the parameters along with the signature to the blockchain, paying for gas. The signature guarantees that the message was approved by the user.
Refund used gas at the end of the transaction. A modifier refundGasCost can be used for this (see below).
But (1) is really hard to apply to token transfers where you just don't know who uses the token and (2) does not really address the issue.
There is a lot happening recently, there is this blog post about How to save your Ethereum Dapp users from paying gas for transactions, and since you ask about tokens, there is an ERC that suggests to Pay transfers in tokens instead of gas, in one transaction which would be nice if you have tokens but no ETH.
I hope this helps.
Exactly this case is already defined in the ERC20 standard. Its this function:
function transferFrom(address from, address to, uint tokens) public returns (bool success);
But before party C could use it and send tokens from A to B, A would have to approve C to do this via the following function, which is also defined in the ERC20 standard:
function approve(address spender, uint tokens) public returns (bool success);
No, in a standard ERC20 token contract, the token holder must initiate at least one transaction (to call transfer() or approve()), and a transaction must always be paid for by its initiator.
This question is a little conceptual, so hopefully this picture will help clear up my misunderstanding.
Image there is a crowdsale smart contract deployed on address 0x2. A User at address 0x01 buys a token.
Here is my understanding of what happens:
The crowdsale contract (# address: 0x2) accepts ether from the user account (# address: 0x1)
The crowdsale contract stores 0x1 as having purchased a token (important: this information is stored in the smart contract #address 0x2)
Now my Question: If 0x1 is a user account (and not a smart contract) there is no code at address 0x1. I thought a user account just consisted of an address + ether associated with the address, how can it also store the fact that 0x1 owns an ERC20 token? For example, I can login to MetaMask and (before clicking the "add token" option) MetaMask can see that I have a token... how is this possible?
Every ERC20 contract has the following function:
function balanceOf(address _owner) public view returns (uint256 balance) {
return balances[_owner];
}
Your wallet just calls this function from the known token contracts with your address. Since it's a view function it doesn't cost any gas.
I recon most ERC20 token get added rather quickly to a wallet like Metamask or MEW. But if your balance doesn't automatically show, you can add the contract address manually (in MEW at least, not sure about Metamask) and it will show up afterwards.
In solidity there are two ways to get the address of the person who sent the transaction
tx.origin
msg.sender
In your example, in the method inside ERC20 Token.sol, the value tx.origin will be 0x1 and msg.sender will be 0x2
So to answer your question, how does the ERC20 token know about 0x2 is: it depends on how the token contract is written and whether it uses tx.origin or msg.sender. I would imagine it uses msg.sender, because that is the more prevalent one.
If it does use msg.sender you can still make the crowdsale contract work by first buying the tokens and then immediatelly transfering the tokens from the crowdsale contract to the caller.
For more information, refer to What's the difference between 'msg.sender' and 'tx.origin'?
how can it also store the fact that 0x1 owns an ERC20 token?
Token transfers, or transfers in accounting in general, are kept in a ledger. In this case, the ledger is ERC-20 smart contract that internally keeps balances who owns and what in its balances mapping. Or, the smart contract manage the storage (EVM SSTORE instructions) where the records of ownership are kept.
Note that some other blockchains, like Telos and EOS (and mayne Solana) might be opposite and there the storage is maintained on the user account (user account has associated RAM and tables for any token user owns).
Since creating a smart contract with Ethereum involves the user of ether, refilling all of the users' ethers becomes costly for a company. So let's say a company decide to issue a token over the ethereum network, and that token represents a new currency. Can the original creator of the token receive transaction fees everytime each user send tokens to someone else? That way the company could easily refill everyone's token's with ether.
You can't receive Ether paid for gas spent on that transaction, it all goes to the miner of current block.
But you can add support for that fee into your token contract. For example you can require to send some Ether with each token transfer, and then automatically send that Ether value into Token contract itself, or send to some other address.
Something like that:
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
// accept fees
if (msg.value < FEE) {
return false;
}
if (!MYADDR.send(msg.value) {
throw;
}
// do token transfer (WARNING, no validation here, don't use, it's for current example only)
balances[_to] += _value;
balances[_from] -= _value;
return true;
}
If you look at the problem as a whole, every user should spend some ether (as fees) to perform any transaction. If you are planning to fill the users accounts' with ether paid by users, the net sum is zero (looking at all users as an entity and company as another entity). So, either you have to fill the users accounts with ether from your pocket or Users have to burn their own pockets to make transactions (transfer tokens etc.)