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I'm trying to upgrade a flashloan file from my study and I don't get one moment about checking pool existence. Here is the code.

// Get the Factory Pair address for combined tokens
        address pair = IUniswapV2Factory(UNISWAP_FACTORY).getPair(
            _tokenBorrow,
            WETH
        );

        // Return error if combination does not exist
        require(pair != address(0), "Pool does not exist");

        // Figure out which token (0 or 1) has the amount and assign
        address token0 = IUniswapV2Pair(pair).token0();
        address token1 = IUniswapV2Pair(pair).token1();
        uint256 amount0Out = _tokenBorrow == token0 ? _amount : 0;
        uint256 amount1Out = _tokenBorrow == token1 ? _amount : 0;

        // Passing data as bytes so that the 'swap' function knows it is a flashloan
        bytes memory data = abi.encode(_tokenBorrow, _amount, msg.sender);

        // Execute the initial swap to get the loan
        IUniswapV2Pair(pair).swap(amount0Out, amount1Out, address(this), data)

In my study file we always borrow USDC, so pair USDC/Weth exists and pair != address(0) But when the borrowed coin is WETH I receive an error : VM Exception while processing transaction: reverted with reason string 'Pool does not exist' As I understand this situation we need to check the existence of this tokenBorrow/WETH pair to be sure that we can borrow a token. But what should I do with WETH? Maybe I should check WETH/ETH pair? But ETH and WETH have the same addresses so I'm stuck here.

1 Answer 1

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Seems like I found an answer after 5 hours of thinking :

if (_tokenBorrow == address(WETH)) {
        address pair = IUniswapV2Factory(UNISWAP_FACTORY).getPair(
        address(WETH),
        _token2
    );

Now I get Uniswap:Locked error. But it seems like uniswap simply needs an existing pair to start swapping. And if I give give him address of this pair it works.

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