Issue in exercise 2,

[farman1094]

I am facing this issue of exercise 2
I am also trying the same thing in other test file which is available here link that is working absolutely fine, I have also tried changing the order of swapExactTokensForTokens and swapTokensForExactTokens function. By calling the function swapTokensForExactTokens first. that also work. But only this specific order is not working down below. Maybe I am missing something important.

Repo Link: https://github.com/farman1094/UniswapV2Practice

code

pragma solidity 0.8.24;
import {Test} from "forge-std/Test.sol";
import {console} from "forge-std/console.sol";

import {IERC20} from "lib/forge-std/src/interfaces/IERC20.sol";
import {IUniswapV2Router02} from "v2-periphery/contracts/interfaces/IUniswapV2Router02.sol";
import {WETH, DAI, MKR, UNISWAP_V2_ROUTER_02 } from "src/constants.sol";
import {IWETH} from "src/interface/IWETH.sol";

contract IssueInTest is Test {

IUniswapV2Router02 public router = IUniswapV2Router02(UNISWAP_V2_ROUTER_02);
IWETH public weth = IWETH(WETH);
IERC20 public dai = IERC20(DAI);
IERC20 public mkr = IERC20(MKR);

address private constant user = address(100);

function setUp() public  {
    console.log(block.chainid);
    
    deal(user, 100e18);
    assert(user.balance == 100e18);
    vm.startPrank(user);
    weth.deposit{value: 100 ether}();
    weth.approve(address(router), type(uint256).max);
    vm.stopPrank(); 
    
}
        function testSwapExactTokensForIssues() public {
            address[] memory path = new address[](3);
            path[0] = WETH;
            path[1] = DAI;
            path[2] = MKR;
            uint deadline = block.timestamp + 1000;
            uint amountIn = 1e18;
            uint amountOutMin = 1;

            vm.prank(user);
            uint[] memory amounts = router.swapExactTokensForTokens(
                amountIn,
                amountOutMin,
                path,
                user,
                deadline
            );

            uint amountOut = 1e17;
            uint amountInMax = 50e18;
            vm.prank(user);
            uint[] memory amountsOut = router.swapTokensForExactTokens(
                amountOut,
                amountInMax,
                path,
                user,
                deadline
            );

            console.log("amounts: WETH", amounts[0]);    
            console.log("amounts: DAI", amounts[1]);    
            console.log("amounts: MKR", amounts[2]);    
        }
}

 ├─ [3534] 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D::swapTokensForExactTokens(100000000000000000 [1e17], 50000000000000000000 [5e19], [0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2, 0x6B175474E89094C44Da98b954EedeAC495271d0F, 0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2], 0x0000000000000000000000000000000000000064, 1732807287 [1.732e9])
    │   ├─ [504] 0x517F9dD285e75b599234F7221227339478d0FcC8::getReserves() [staticcall]
    │   │   └─ ← [Return] 0x0000000000000000000000000000000000000000000000d511fd926ed23d45b300000000000000000000000000000000000000000000000000481274e527b948000000000000000000000000000000000000000000000000000000006748868f
    │   └─ ← [Revert] revert: ds-math-sub-underflow
    └─ ← [Revert] revert: ds-math-sub-underflow

Suite result: FAILED. 0 passed; 1 failed; 0 skipped; finished in 13.77s (7.95s CPU time)

Ran 1 test suite in 15.36s (13.77s CPU time): 0 tests passed, 1 failed, 0 skipped (1 total tests)

Failing tests:
Encountered 1 failing test in test/IssueInTest.t.sol:IssueInTest
[FAIL: revert: ds-math-sub-underflow] testSwapExactTokensForIssues() (gas: 170738)```

[EngrPips]

This works fine for me.

Ran 1 test for test/UniswapV2SwapTest.t.sol:UniswapV2SwapTest
[PASS] test_swapTokensForExactTokens() (gas: 164757)
Logs:
  WETH 94124367944473348
  DAI 337407440607281150345
  MKR 100000000000000000

Traces:
  [62118] UniswapV2SwapTest::setUp()
    ├─ [0] VM::deal(0x0000000000000000000000000000000000000064, 100000000000000000000 [1e20])
    │   └─ ← [Return] 
    ├─ [0] VM::startPrank(0x0000000000000000000000000000000000000064)
    │   └─ ← [Return] 
    ├─ [23974] 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2::deposit{value: 100000000000000000000}()
    │   ├─ emit Deposit(param0: 0x0000000000000000000000000000000000000064, param1: 100000000000000000000 [1e20])
    │   └─ ← [Stop] 
    ├─ [24420] 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2::approve(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D, 115792089237316195423570985008687907853269984665640564039457584007913129639935 [1.157e77])
    │   ├─ emit Approval(owner: 0x0000000000000000000000000000000000000064, spender: 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D, value: 115792089237316195423570985008687907853269984665640564039457584007913129639935 [1.157e77])
    │   └─ ← [Return] true
    ├─ [0] VM::stopPrank()
    │   └─ ← [Return] 
    └─ ← [Stop] 

  [170357] UniswapV2SwapTest::test_swapTokensForExactTokens()
    ├─ [0] VM::prank(0x0000000000000000000000000000000000000064)
    │   └─ ← [Return] 
    ├─ [156224] 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D::swapTokensForExactTokens(100000000000000000 [1e17], 1000000000000000000 [1e18], [0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2, 0x6B175474E89094C44Da98b954EedeAC495271d0F, 0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2], 0x0000000000000000000000000000000000000064, 1732802447 [1.732e9])
    │   ├─ [2504] 0x517F9dD285e75b599234F7221227339478d0FcC8::getReserves() [staticcall]
    │   │   └─ ← [Return] 375666095063796494027 [3.756e20], 211674029428388778 [2.116e17], 1732785371 [1.732e9]
    │   ├─ [2504] 0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11::getReserves() [staticcall]
    │   │   └─ ← [Return] 6552852397611689605386392 [6.552e24], 1822428920933467739475 [1.822e21], 1732802243 [1.732e9]
    │   ├─ [15025] 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2::transferFrom(0x0000000000000000000000000000000000000064, 0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11, 94124367944473348 [9.412e16])
    │   │   ├─ emit Transfer(from: 0x0000000000000000000000000000000000000064, to: 0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11, value: 94124367944473348 [9.412e16])
    │   │   └─ ← [Return] true
    │   ├─ [48033] 0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11::swap(337407440607281150345 [3.374e20], 0, 0x517F9dD285e75b599234F7221227339478d0FcC8, 0x)
    │   │   ├─ [13074] 0x6B175474E89094C44Da98b954EedeAC495271d0F::transfer(0x517F9dD285e75b599234F7221227339478d0FcC8, 337407440607281150345 [3.374e20])
    │   │   │   ├─ emit Transfer(from: 0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11, to: 0x517F9dD285e75b599234F7221227339478d0FcC8, value: 337407440607281150345 [3.374e20])
    │   │   │   └─ ← [Return] true
    │   │   ├─ [602] 0x6B175474E89094C44Da98b954EedeAC495271d0F::balanceOf(0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11) [staticcall]
    │   │   │   └─ ← [Return] 6552514990171082324236047 [6.552e24]
    │   │   ├─ [534] 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2::balanceOf(0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11) [staticcall]
    │   │   │   └─ ← [Return] 1822523045301412212823 [1.822e21]
    │   │   ├─ emit Sync(reserve0: 6552514990171082324236047 [6.552e24], reserve1: 1822523045301412212823 [1.822e21])
    │   │   ├─ emit Swap(sender: 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D, amount0In: 0, amount1In: 94124367944473348 [9.412e16], amount0Out: 337407440607281150345 [3.374e20], amount1Out: 0, to: 0x517F9dD285e75b599234F7221227339478d0FcC8)
    │   │   └─ ← [Stop] 
    │   ├─ [67846] 0x517F9dD285e75b599234F7221227339478d0FcC8::swap(0, 100000000000000000 [1e17], 0x0000000000000000000000000000000000000064, 0x)
    │   │   ├─ [32706] 0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2::transfer(0x0000000000000000000000000000000000000064, 100000000000000000 [1e17])
    │   │   │   ├─ emit Transfer(from: 0x517F9dD285e75b599234F7221227339478d0FcC8, to: 0x0000000000000000000000000000000000000064, value: 100000000000000000 [1e17])
    │   │   │   └─ ← [Return] true
    │   │   ├─ [602] 0x6B175474E89094C44Da98b954EedeAC495271d0F::balanceOf(0x517F9dD285e75b599234F7221227339478d0FcC8) [staticcall]
    │   │   │   └─ ← [Return] 713073535671077644372 [7.13e20]
    │   │   ├─ [715] 0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2::balanceOf(0x517F9dD285e75b599234F7221227339478d0FcC8) [staticcall]
    │   │   │   └─ ← [Return] 111674029428388778 [1.116e17]
    │   │   ├─ emit Sync(reserve0: 713073535671077644372 [7.13e20], reserve1: 111674029428388778 [1.116e17])
    │   │   ├─ emit Swap(sender: 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D, amount0In: 337407440607281150345 [3.374e20], amount1In: 0, amount0Out: 0, amount1Out: 100000000000000000 [1e17], to: 0x0000000000000000000000000000000000000064)
    │   │   └─ ← [Stop] 
    │   └─ ← [Return] [94124367944473348 [9.412e16], 337407440607281150345 [3.374e20], 100000000000000000 [1e17]]
    ├─ [0] console::log("WETH", 94124367944473348 [9.412e16]) [staticcall]
    │   └─ ← [Stop] 
    ├─ [0] console::log("DAI", 337407440607281150345 [3.374e20]) [staticcall]
    │   └─ ← [Stop] 
    ├─ [0] console::log("MKR", 100000000000000000 [1e17]) [staticcall]
    │   └─ ← [Stop] 
    ├─ [715] 0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2::balanceOf(0x0000000000000000000000000000000000000064) [staticcall]
    │   └─ ← [Return] 100000000000000000 [1e17]
    ├─ [0] VM::assertEq(100000000000000000 [1e17], 100000000000000000 [1e17], "MKR balance of user") [staticcall]
    │   └─ ← [Return] 
    └─ ← [Stop] 

Suite result: ok. 1 passed; 0 failed; 0 skipped; finished in 12.52s (8.42s CPU time)

[EngrPips]

Hello @farman1094, can you find where this error ds-math-sub-underflow is in your codebase? It will help us get a good understanding of what is causing the revert.

[farman1094]

Hello @farman1094, can you find where this error ds-math-sub-underflow is in your codebase? It will help us get a good understanding of what is causing the revert.

As per my knowledge it's causing here

[EngrPips]

Where in the below image does it revert with ds-math-sub-underflow?

For the second swap that is failing, You should capture the amountOut that is required for the amountIn that you want and see if your balance covers the required amountIn

[t4sk]

Hello @farman1094, can you find where this error ds-math-sub-underflow is in your codebase? It will help us get a good understanding of what is causing the revert.

That is an error from Maker DAO code. Either DAI or MKR token

[EngrPips]

Hello @farman1094, can you find where this error ds-math-sub-underflow is in your codebase? It will help us get a good understanding of what is causing the revert.

That is an error from Maker DAO code. Either DAI or MKR token

Interesting. Thanks for pointing this out sir.

[t4sk]

@farman1094
Issue was low liquidity on Uni v2 DAI/MKR
It should now be fixed

[EngrPips]

Interesting.

[Nika250]

Thank you, I found the answer!

[MattCrBoom]

👍 nice