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
-
daiAmount
is amount of Dai which user is going to pay. -
deadline
is time limit for transaction
-
path
is 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);
β How do you know the number of path my trade takes?
-
As we convert ETH to DAI, first value of
path
is address of WETH, second value ofpath
is 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);
β 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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