Token (solidity) - Reward a user X amount of token from main app wallet with user paying the gas

Question

Hello Everything is fine?

I'm now starting to study Solidity, I'm making a centralized game, and after some successful missions, I want to give the user the option of "Claim tokens", where I would transfer from the game wallet to him, and the amount is the backend that define, how would I go about implementing this? (My question is how to create a function in the contract where the amount is authorized by the backend somehow)

Answer 1

After a lot of searching I found the answer in Solidity's documentation, what I wanted is item 3.3.4 (Micropayment channel) of the documentation (readthedocs.org/projects/solidity/downloads/pdf/v0.5.12), there it explains how to authorize a person to withdraw from the my wallet with signatures and hash, without me needing to call even a method of the contract

Answer 2

You can create a function executable by the user (so that they pay the gas fees) that makes use of the ERC-20 transfer() function (assuming your tokens are going to be ERC-20).

In this example, anytime the user executes the claimToken() function, they are going to receive claimAmount of tokens from the MyGame contract address.

For the authorization, I used the Ownable pattern, where only an authorized address can execute the function (in this case setClaimAmount()).

pragma solidity ^0.8;

interface ITokenContract {
    function transfer(address _receiver, uint256 _amount) external returns (bool);
}

contract MyGame {
    ITokenContract tokenContract = ITokenContract(address(0x123));
    uint256 public claimAmount;
    address public owner;
    
    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    function claimTokens() external {
        // send `claimAmount` of tokens from this contract address
        // to the user executing the `claimTokens()` function
        bool success = tokenContract.transfer(msg.sender, claimAmount);
        require(success);
    }
    
    function setClaimAmount(uint256 _claimAmount) external onlyOwner {
        claimAmount = _claimAmount;
    }
}

Also, you'll might want to implement some validation to the claimTokens() function, so that they don't perform the transfer more often than you'd like to.