I am learning solidity and want to create a contract that will lock token for Uniswap LP. What I've created is:
List item
on token creation I am creating uniswap pair with that token
I am creating a Timelock for token amount assigned to creator address
now on release() method I would like to automatically add liquidity with eth value that has been sent and token that was locked
Problem here is that to add LP to uniswap token needs to be approved and from what I see the only way to approve token is to first send this token to creator address.
Is it possible to make it automatic so that we don't need to trust contract creator to add LP after it has been released to him?
You can have non-standard ERC-20 token that allows perform approve for Uniswap contract addresses on special conditions (e.g. before a certain time or similar).
You would directly update allowances table in your token. You do not need to use approve() from ERC-20 because it is your token.
Related
I would like to transfer ERC20 tokens from a wallet who don't own ETH to another wallet who own ETH and who can pay gas fee.
Do you know if it is possible to made a transfer of ERC20 tokens and to let the receiver wallet pay fees ?
TLDR: Not possible, unless the token contract explicitly allows it. Or unless the token holder is also the block producer.
Transaction fees are paid in ETH (or generally, native currency of the network - for example BNB on Binance Smart Chain, MATIC on Polygon, ...). So in most cases, you need to pay ETH to execute either the transfer() function if you want to send the tokens from your address, or the approve() function if you want someone else to transfer tokens from your address.
Very few token contracts implement delegated transfer mechanism on top of the ERC20 standard. There's currently no standardized way to perform a delegated transfer, so each contract might have a different implementation. The token holder uses their private key to sign a predetermined message saying how many tokens they want to transfer to which address. The message also usually contains a nonce or a timestamp to prevent signature replay attack. Token holder passes the message offchain to the transaction sender, and then the transaction sender executes a function of the token contract built specifically for delegated transfers (note that the transaction sender pays the fee to execute this function). The contract validates the signature, and performs the transfer. Again, most token contracts do not implement this mechanism.
One more exception from the rule is a block producer. When you create a new block, you can fill it with transactions not only from the mempool but also with your own transactions. You can build a transaction with 0 gas price, and then include it in the block that you're producing. This way you're also able to send tokens for free.
I'm building a DeFi application on Ethereum, and I would like to implement the Deposit function. Everything works fine between ETH and a ERC20 token that I built, but I would like to add some tokens like aToken for AAVE or cTokens for Compound that the user will receive after a Deposit call.
So the question is: is it possible to add a function in my smart contract to create multiple tokens without creating a smart contract for each of them? If not, I have to create a different contract for each token I want to add in my app or there is a best method to do it?
Yes this is possible. You can transfer the tokens to the user's address after the Compound Protocol mint operation. This can be made generic using the ERC-20 transfer interface. Be sure to account the amounts users are due and beware of the reentrancy vulnerability.
If you are using the ERC-721 standard, what is the prefer method determining which tokens the address owns in a DAPP.
Currently I'm request all the Transfer Events for an address and basically sorting them into transfer in and transfer out, and then using that to determine which tokens the user owns.
Is there a simpler way I missed.
Transfer events may be emitted also by contracts that are not ERC-721 tokens, or some noname tokens that you might not be interested in.
The actual token ownership is stored in the tokens contracts (and not the DAPP contract).
So your current approach is pretty much as straightforward as it can get, if you want to automatically keep track of all tokens that the address currently owns (and some false positives as well).
Note: This is also similar to the approach of Etherscan, which listens to all Transfer event logs and if the sender contract is listed in their database of tokens, they use the event log data to update balances of the sender and recipient.
If you're willing/able to create and maintain a list of tokens that you want to follow, I'd recommend a simpler approach:
Define the list of followed token contract addresses (e.g. ECF or RARI)
For each of these token contracts, call balanceOf(<your_dapp_address>) that returns amount of tokens that the <your_dapp_address> currently owns.
Everyone can create ethereum token by solidity codes but don't know how can this token integrate as payment gateway in ecommerce website.
For real project . This token need frontend web wallet /android wallet and integration to every website as payment.
Plz suggest me .how can find this way.
What need more to study.
Token is not a payment gateway. If i understand your question correctly, you are asking, how can you interact with a token that you have created through Solidity from frontend. One use case would be how people can use the token that you have created to purchase some item. For this the users should already be holding the tokens. This can be bought from an ICO or from an exchange. Basically there's a couple of functions in ERC20 token i.e., approve() and transfer() that will approve apps like exchanges to perform transactions on behalf of the owner of the token. Once the users have those tokens they can purchase items from it. Again, you have to write the logic how and what you expect users to do.
ERC20 Token is works likes Currency.And solidity is a programming language. which we used for write the smart contract. if you want to invoke your function then you need to create wallet account ,after that you can do transaction using with web3js. you can get ether for testing purpose from faucet.Basically these are functions in ERC20 token i.e., approve() and transfer() that will perform transactions
I don't suggest using ERC20 tokens as payment method.
Ethereum network is not fast enough,you need 30 confirmations to make sure you received the token, some times the delay can be 1 day
Cost is high, when you transfer token ,usually you have a smart contract, it costs lots of gas
Ether price is not stable, it drops 90% of value from Jan 2018 to Dec 2018. it will be hard for estore to maintain profit.
However if you still want to do that, yes, you can create your own gateway using tokens as your accepted currency.
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).