i want to mint tokens for an address. For example, suppose I have your wallet address. Now I want to mint 10 ERC20 tokens to your account. The gas fee should be deducted from your account. Now, you are aware that I am going to mint(buy) 10 tokens for you but you don't know when. I don't want you to wait for me that when will I mint tokens on your behalf. So whenever I mint, the minting should be successful and does not require your approval while minting.
So, summarising, I minted(buyed) 10 tokens from your account and the gas fee is deducted from your account and now you will have 10 tokens. Can I write a function like this in solidity.
There are multiple options that you can choose
Option 1
Use a Gas station network. GSN's enable relaying signed transactions and therefore enable paying for the gas in the relay.
Option 2
Mint when the user calls the function, but lock them until you want them to be tradable
Option 3
Write your mint function to mint anything to the contract address. Then, when you want it to be received by the user, transfer them to the user.
Option 4
While the user wants to mint and calls the function, you can request some amount in ether that will approximately cover for the gas that will be used once it is minted. Keep that ether in contract, and once you mint it literally, use that gas.
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 am learning node JS developing a crypto currency exchanger as a homework project where user can deposit ERC-20 token and Ethereum. I am generating unique ethereum deposit address for every user, where they can deposit ERC-20 token and ethereum. but after sometime I want to move the received ethereum and ERC-20 token to another address (cold wallet).
If someone only send ERC-20 token to the address and no etherum, then how I'll get ethereum to pay as gas fee to transfer the received ERC-20 token to cold wallet?
If suppose, I am first paying etherum (for gas fee) from cold address to the user address, and then using that etherum to transfer received ERC-20 token, will it work at mass level ? means if 10000 users do the same thing at the same time, will not it create a problem ? or is there any better solution for this?
If there's no eth in that account, you can't take the ERC-20 token out.
Transfer some eth to the address and then get ERC-20 token out is the only way. The problem is how to save the gas as far as you can.
You can write a batch transfer contract to send eth to several hundred addresses in one go (the ceiling is determined by block gas limit), batch transfer saves gas. Then you can collect the ERC-20 tokens.
Of course, you can charge your user for compensation.
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.
Users can deposit on Binance, for example, various ERC20 tokens, but later then those tokens should be transferred to the Binance cold wallet(wallet used for withdrawing) how those tokens are transferred when the newly generated address doesn't contain any ether(for transferring contracts), it doesn't make any sense for me that Binance sends some ether for every newly generated address.
it doesn't make any sense for me that Binance sends some ether for every newly generated address.
That's exactly what they do. If you do happen to deposit ether, they will leave a little bit ~$5 or so in the address when moving the ether to their cold wallet to pay for future token transactions. If you transfer only tokens, they will transfer some ETH before moving it.
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).