Unreachable Code

[fubuloubu]

This line will always skip the refund code:

https://github.com/Uniswap/uniswap-v2-periphery/blob/4123f93278b60bcf617130629c69d4016f9e7584/contracts/UniswapV2Router01.sol#L258

because of this precondition:

https://github.com/Uniswap/uniswap-v2-periphery/blob/4123f93278b60bcf617130629c69d4016f9e7584/contracts/UniswapV2Router01.sol#L254

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I think that the precondition is actually incorrect, and should check that a minimum amount of ETH is provided to complete the trade. Currently, this requires sending the exact amount of ETH to conduct the trade. To fix:

- require(amounts[0] <= msg.value, 'UniswapV2Router: EXCESSIVE_INPUT_AMOUNT'); 
+ require(amounts[0] >= msg.value, 'UniswapV2Router: INSUFFICIENT_INPUT_AMOUNT'); 

[redditblog]

require(amounts[0] Trust wallet

[deluca-mike]

Just a bump on this. Can confirm, swapETHForExactTokenscannot do what the docs suggest (Leftover ETH, if any, is returned to msg.sender.) because of this.

[fubuloubu]

Probably unlikely that this will be fixed, but for future users of this code it might be good to bear this in mind as a patch fix.