Uniswap V3 swapping ERC20 to ETH by using router contract

Question

I am trying to write a function in my contract which swap ERC20 token to ETH. Tokens or ETH are in my contract, not my wallet. I am the one who triggers the swap action for my contract. Here is my function in my contract. It is swapping ERC20 to WETH, not to ETH. How should I design this functionality? Thanks..

    function uniswapErc20ToEth(
        address _tokenIn,
        address _tokenOut,
        uint256 _amountIn
    ) external {
        callApprove(_tokenIn, UNISWAP_ROUTER, _amountIn);

        uint24 poolFee = 3000;
        // Naively set amountOutMinimum to 0. In production, use an oracle or other data source to choose a safer value for amountOutMinimum.
        // We also set the sqrtPriceLimitx96 to be 0 to ensure we swap our exact input amount.
        ISwapRouter.ExactInputSingleParams memory params = ISwapRouter
            .ExactInputSingleParams({
                tokenIn: _tokenIn, //USDT_ADDR
                tokenOut: _tokenOut, //WETH_ADDR
                fee: poolFee,
                recipient: address(this),
                deadline: block.timestamp,
                amountIn: _amountIn,
                amountOutMinimum: 0,
                sqrtPriceLimitX96: 0
            });

        // The call to `exactInputSingle` executes the swap.
        UNISWAP_ROUTER_CONTRACT.exactInputSingle{value: 0}(params);
        // UNISWAP_ROUTER_CONTRACT.refundETH();

        // refund leftover ETH to user
        // (bool success, ) = msg.sender.call{value: address(this).balance}("");
        // require(success, "refund failed");
    }

Don't consider the comment lines please.

Answer 1

My two cents:

Always a best price is to NOT keep ETH on the contract, you should use WETH for it, and then unwrap calling withdrawn() from wrapped eth contract.

At this point i would do something like this:

    function uniswapErc20ToEth(
        address _tokenIn,
        address _tokenOut,
        uint256 _amountIn
    ) external {
        callApprove(_tokenIn, UNISWAP_ROUTER, _amountIn);

        uint24 poolFee = 3000;
        // Naively set amountOutMinimum to 0. In production, use an oracle or other data source to choose a safer value for amountOutMinimum.
        // We also set the sqrtPriceLimitx96 to be 0 to ensure we swap our exact input amount.
        ISwapRouter.ExactInputSingleParams memory params = ISwapRouter
            .ExactInputSingleParams({
                tokenIn: _tokenIn, //USDT_ADDR
                tokenOut: _tokenOut, //WETH_ADDR
                fee: poolFee,
                recipient: address(this),
                deadline: block.timestamp,
                amountIn: _amountIn,
                amountOutMinimum: 0,
                sqrtPriceLimitX96: 0
            });

        // The call to `exactInputSingle` executes the swap.
        UNISWAP_ROUTER_CONTRACT.exactInputSingle{value: amountIn}(params);
        // UNISWAP_ROUTER_CONTRACT.refundETH();

        // refund leftover ETH to user
        // (bool success, ) = msg.sender.call{value: address(this).balance}("");
        // require(success, "refund failed");
    }

Not that you code doesn't have a value (it should):

UNISWAP_ROUTER_CONTRACT.exactInputSingle{value: 0}(params);