web3-starter-sol/advanced_knowledge/saving_gas/gasless_token_transfer.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;

// gaslless erc20 token transfer with meta transaction

interface IERC20Permit {
    function totalSupply() external view returns (uint256);

    function balanceOf(address account) external view returns (uint256);

    function transfer(address recipient, uint256 amount) external returns (bool);

    function allowance(address owner, address spender) external view returns (uint256);

    function approve(address spender, uint256 amount) external returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract GaslessTokenTransfer {
    function send(
        address token,
        address sender,
        address receiver,
        uint256 amount,
        uint256 fee,
        uint256 deadline,
        // Permit signature
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external {
        // Permit
        IERC20Permit(token).permit(
            sender,
            address(this),
            amount + fee,
            deadline,
            v,
            r,
            s
        );
        // Send amount to receiver
        IERC20Permit(token).transferFrom(sender, receiver, amount);
        // Take fee - send fee to msg.sender
        IERC20Permit(token).transferFrom(sender, msg.sender, fee);
    }
}