How to avoid second confirmation of Metamask on DEX swaping ?

[biahoi]

HI,
I am coding a bot program that interacts with Pancakeswap router to make a SwapExacTokensToTokens when a good price came.
The intended work flow is:
(1) User approves the fund on Metamask to be used by Pancakeswap Router; During this procedure, Metamask will have a pop up dialog to ask user to click Confirm button
(2) Bot handle trading logics and when time is come:
(3) Bot cal SwapExacTokensToTokens on Router contract. But then the Metamask dialog box is poping up once again, requiring user to click the button (!?) How can I avoid this second time approval request?

My code looks like this for now:

`
async function swapFunction() {

    const BASE = "0xbb4cdb9cbd36b01bd1cbaebf2de08d9173bc095c";

    const TOKEN = "0xe9e7cea3dedca5984780bafc599bd69add087d56";

    const ROUTER_ADDR = '0x05ff2b0db69458a0750badebc4f9e13add608c7f'; //pancakeswap router

    const provider = new ethers.providers.Web3Provider(window.ethereum)

    const signer = provider.getSigner()

    const signerAddress = await signer.getAddress()

    const ACCOUNT = provider.getSigner(0);
    

    var ROUTER_CONTRACT = await new ethers.Contract(
        ROUTER_ADDR,
        [
        'function getAmountsOut(uint amountIn, address[] memory path) public view returns (uint[] memory amounts)',
        'function swapExactTokensForTokens(uint amountIn, uint amountOutMin, address[] calldata path, address to, uint deadline) external returns (uint[] memory amounts)',
        ],
        ACCOUNT
        );


    var BASE_CONTRACT = new ethers.Contract(
        BASE,
        [
        'function approve(address spender, uint value) external returns (bool)',
        'function decimals() public view returns (uint8)',
        'function balanceOf(address account) external view returns (uint256)',
        'function allowance(address _owner, address spender) external view returns (uint256)'
        ],
        ACCOUNT
        );

    var amountIn_weiBN = ethers.utils.parseEther("0.001");
    var gasLimit = 300000;
    var gasPrice_weiBN = ethers.utils.parseUnits(`${5}`, 'gwei');;
    var approved = false

    // ******************  Here Metamask ask to Click Confirmation 1st time. *******************
    var approved = await BASE_CONTRACT.approve( ROUTER_ADDR,
                                            amountIn_weiBN,
                                            {
                                            'gasLimit': gasLimit,
                                            'gasPrice': gasPrice_weiBN 
                                            });


    
    var routerAmountsOutBN = await ROUTER_CONTRACT.getAmountsOut( amountIn_weiBN,  [BASE, TOKEN]);
    

   
   // .... Here will come some bot logics .... 
   // How to avoid this second time Confirmation ??
   // ******************  Here Metamask ask to Click Confirmation 2nd time. *******************

    var tx = await ROUTER_CONTRACT.swapExactTokensForTokens(
                  routerAmountsOutBN[0],
                  routerAmountsOutBN[1],
                  [BASE, TOKEN],
                  signerAddress,
                  Date.now() + 1000 * 60 * 10, //10 minutes
                  {
                    'gasLimit': gasLimit,
                    'gasPrice': gasPrice_weiBN
        })
    
    
  }`

[zemse]

Seems your bot is on the frontend itself and sending tx using user's wallet. Metamask asks this for safety of the user. Imagine going to a random site and then funds move out of user's wallet without asking for confirmation.

What you could do is move user's funds to a temporary wallet (ethers.Wallet.createRandom()), and then when your bot figures out the right time to put up a trade, it would send the transaction from that temp wallet, since this is not going through metamask it wouldn't ask for confirmation. Also, make sure that you back up the keys for the temp wallet before moving any funds in it since it can get lost when the page refreshes.

[ricmoo]

I would suggest one slightly different step based on this method, which is instead of moving the funds, simply approve the random Wallet to move the funds. That way if you lose the random wallet, you don’t lose access.

Obviously any solution which does not prompt for the user needs a great deal of thought security-wise; e.g. how do you convince the user to trust the key was created randomly and you aren’t secretly an attacker with that private key ready to ponce and steal their funds. You would also need ether sitting at that account to actually execute the transaction too.

[biahoi]

Do you mean, at first user will approve the random wallet to use the fund. Then, when time is come, this wallet will withdraw fund from MM then right after that make a swap with Dex, and then transfer back new token to MM? But isn't it will triger another confirmation pop up from MM when it withdraw the fund from MM?

[biahoi]

I see BoggedFinance they solved this problen some how, user just have to click approval once until the swap is done by the site.. @zemse , and tokens did not moved until the actual swap

[zemse]

@biahoi Yeah, they likely must be having their own smart contract over there and the user approves that contract instead of Uniswap Router. So when it's the time, their system must be calling a method on their smart contract, which moves funds out from your wallet (here metamask is not involved as you already approved tokens for spending, so it's how erc20 works). The only catch here is that, system needs to pay gas fees in ETH to trigger the trade, and hence they have to take the cut from the trade equivalent to the gas paid. This seems to bring an element of centralization though