ERC20AntiSandwich

Never get jared again.

This project demonstrates a basic ERC20 token use case. It comes with a special modifier for the transfer and transferFrom functionality. The modifier "onlyOncePerBlock(address,address)" will make a token sender only be able to send a transfer transaction once per block. A sandwich (front- & backrun within one block) isn't possible anymore. Although a single frontrun or a backrun will still be possible.

Magic modifier

mapping(bytes32 => bool) private perBlock;
mapping(address => bool) private exceptions;
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...
modifier onlyOncePerBlock(address _from, address _to) {
    if (!exceptions[_from]) {
        bytes32 key = keccak256(abi.encodePacked(block.number, _from));
        require(!perBlock[key], "ERC20: Only one transfer per block per address");
        perBlock[key] = true;
    }
    if (!exceptions[_to]) {
        bytes32 key = keccak256(abi.encodePacked(block.number, _to));
        require(!perBlock[key], "ERC20: Only one transfer per block per address");
        perBlock[key] = true;
    }
    _;
}
...
...
...
function _beforeTokenTransfer(address from, address to, uint256 amount) internal whenNotPaused onlyOncePerBlock(from,to) override {
    super._beforeTokenTransfer(from, to, amount);
}

Getting started

1. Download NodeJS and install it
2. Open terminal and navigate to the project directory
3. Run npm install

Deploy SafeMEME (an example ERC20AS token)

1. Open .env file and edit ALCHEMY_KEY to your Alchemy API key
2. Run npx hardhat compile to compile the contract
3. Run npx hardhat test to test the contract

Todo's

• Create a working ERC20 boiler plate
• Optimize modifier onlyOncePerBlock for gas (currently a transfer costs 103.165)
• Implement a version without the need of modifying the state (removing mapping exceptions)