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Sources
Using the new Uniswap v2 in your contracts
Pay
Allow users to pay ETH instead of DAI to service.
function pay(uint paymentAmountInDai) public payable {
if (msg.value > 0) {
convertEthToDai(paymentAmountInDai);
} else {
require(daiToken.transferFrom(msg.sender, address(this), paymentAmountInDai);
}
// do something with that DAI
...
}
convertEthToDai
Paramters
-
daiAmountis amount of Dai which user is going to pay. -
deadlineis time limit for transaction
-
pathis array of token address that involves in exchage. For example, ETH can be first traded to WETH, then WETH traded to USDC, then USDC to Dai (for example).
address[] memory path = new address[](2);→ How do you know the number of path my trade takes?
-
As we convert ETH to DAI, first value of
pathis address of WETH, second value ofpathis address of DAI. Be careful that we deal with WETH, not ETH itself.
path[0] = uniswapRouter.WETH(); path[1] = daiToken; -
Swap ETH for exact amount of tokens. ETH are given by
msg.value.
uniswapRouter.swapETHForExactTokens.value(msg.value)(daiAmount, path, address(this), deadline);→ syntax?
-
Refund leftover ETH to user(
msg.sender).
msg.sender.call.value(address(this).balance)("");
getEstimatedETHforDAI
Calculate the amount of ETH user has to pay.
Use getAmountsIn function to calculate the optimal input amount for given DAI amount of daiAmount .
function getEstimatedETHforDAI(uint daiAmount) public view returns (uint[] memory) {
address[] memory path = new address[](2);
path[0] = uniswapRouter.WETH();
path[1] = multiDaiKovan;
return uniswapRouter.getAmountsIn(daiAmount, path);
}
Example
pragma solidity 0.7.1;
import "https://github.com/Uniswap/uniswap-v2-periphery/blob/master/contracts/interfaces/IUniswapV2Router02.sol";
contract UniswapExample {
address internal constant UNISWAP_ROUTER_ADDRESS = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D ;
IUniswapV2Router02 public uniswapRouter;
address private multiDaiKovan = 0x4F96Fe3b7A6Cf9725f59d353F723c1bDb64CA6Aa;
constructor() {
uniswapRouter = IUniswapV2Router02(UNISWAP_ROUTER_ADDRESS);
}
function convertEthToDai(uint daiAmount) public payable {
uint deadline = block.timestamp + 15; // using 'now' for convenience, for mainnet pass deadline from frontend!
uniswapRouter.swapETHForExactTokens{ value: msg.value }(daiAmount, getPathForETHtoDAI(), address(this), deadline);
// refund leftover ETH to user
(bool success,) = msg.sender.call{ value: address(this).balance }("");
require(success, "refund failed");
}
function getEstimatedETHforDAI(uint daiAmount) public view returns (uint[] memory) {
return uniswapRouter.getAmountsIn(daiAmount, getPathForETHtoDAI());
}
function getPathForETHtoDAI() private view returns (address[] memory) {
address[] memory path = new address[](2);
path[0] = uniswapRouter.WETH();
path[1] = multiDaiKovan;
return path;
}
// important to receive ETH
receive() payable external {}
}
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