Skip to main content

Destination Contract Functions

Overview​

Constructor Function​

UniswapDemoStopOrderCallback.sol
constructor(address _callback_sender, address _router) {
        callback_sender = _callback_sender;
        router = IUniswapV2Router02(_router);
    }

Parameters​

  • _callback_sender: Address of the sender authorized to invoke the stop order function.

  • _router: Address of the Uniswap V2 router contract.

Description​

The constructor function in the UniswapDemoStopOrderCallback.sol contract initializes the contract by setting the callback_sender and router variables. This constructor is called only once during the deployment of the contract. It ensures that the contract is properly configured with the address of the callback sender and the Uniswap V2 router contract, enabling it to execute stop orders on the Uniswap V2 platform. callback_sender sets its variable to the provided _callback_sender address. This address represents the entity authorized to call the stop function. router casts its address to the IUniswapV2Router02 interface, initializing the router variable. This allows the contract to interact with the Uniswap V2 router contract.

stop Function​

UniswapDemoStopOrderCallback.sol
function stop(
        address pair,
        address client,
        bool is_token0,
        uint256 coefficient,
        uint256 threshold
    ) external {
        if (callback_sender != address(0)) {
            require(msg.sender == callback_sender, 'Unauthorized');
        }
        address token0 = IUniswapV2Pair(pair).token0();
        address token1 = IUniswapV2Pair(pair).token1();
        (uint112 reserve0, uint112 reserve1, ) = IUniswapV2Pair(pair).getReserves();
        require(below_threshold(is_token0, Reserves({ reserve0: reserve0, reserve1: reserve1 }), coefficient, threshold), 'Rate above threshold');
        address token_sell = is_token0 ? token0 : token1;
        address token_buy = is_token0 ? token1 : token0;
        uint256 allowance = IERC20(token_sell).allowance(client, address(this));
        require(allowance > 0, 'No allowance');
        require(IERC20(token_sell).balanceOf(client) >= allowance, 'Insufficient funds');
        assert(IERC20(token_sell).transferFrom(client, address(this), allowance));
        assert(IERC20(token_sell).approve(address(router), allowance));
        address[] memory path = new address[](2);
        path[0] = token_sell;
        path[1] = token_buy;
        uint256[] memory tokens = router.swapExactTokensForTokens(allowance, 0, path, address(this), DEADLINE);
        assert(IERC20(token_buy).transfer(client, tokens[1]));
        emit Stop(pair, client, token_sell, tokens);
    }

Parameters​

Parameters:

  • pair: Address of the Uniswap V2 pair contract.

  • client: Address of the client.

  • is_token0: Boolean indicating whether the token being monitored is token0.

  • coefficient: Coefficient value used for comparison.

  • threshold: Threshold value used for comparison.

Description​

This function executes a stop order on the Uniswap V2 decentralized exchange. It ensures that the caller is authorized to execute the stop order, retrieves token addresses from the Uniswap V2 pair contract, checks if the current reserves meet the specified threshold conditions, and performs the swap transaction on behalf of the client. Finally, it emits a Stop event with relevant information about the executed stop order.

below_threshold Function​

UniswapDemoStopOrderCallback.sol
function below_threshold(bool token0, Reserves memory sync, uint256 coefficient, uint256 threshold) internal pure returns (bool) {
        if (token0) {
            return (sync.reserve1 * coefficient) / sync.reserve0 <= threshold;
        } else {
            return (sync.reserve0 * coefficient) / sync.reserve1 <= threshold;
        }
    }

Parameters​

  • token0: Boolean indicating whether the token being monitored is token0.

  • sync: A Reserves struct containing the current reserve values of the pair.

  • coefficient: Coefficient value used for comparison.

  • threshold: Threshold value used for comparison.

Description​

The function calculates whether the current reserves meet the threshold conditions. If the token0 parameter is true, it computes (reserve1 * coefficient) / reserve0 and compares it with the threshold. If token0 is false, it computes (reserve0 * coefficient) / reserve1 and compares it with the threshold. It returns a boolean value indicating whether the current reserves meet the threshold conditions. Internally used within the contract, the function determines whether a stop order should be executed based on the current reserves of the Uniswap pair. Being a pure function, it does not modify the contract state and can be safely called from other functions.