在各個公鏈上都有原生代幣（native cryptocurrency）的存在，以及同質化代幣兩種存在，一種是儲存在區塊鏈錢包之中，而後者則是定義在區塊鏈智能合約的記帳簿裡（某個資料結構）。如果我們需要使用原生代幣和同質化代幣（這邊單指 ERC-20） 互動時，常常會因為各種 interface 沒有相同的原因而需要特別去定義原生代幣的使用標準。
或者在另外一個情況，如果我們需要在 Layer2 或者其他 L1 公鏈中查看 Ethereum 的 ether 在那些鏈上的狀況，就必須在那些鏈上建立一個同質化代幣或類似概念來代表 ether。於是就出現了包裝以太幣（wrapped ETH, WETH），也就是 fungible wrapper。
const balanceOfWETH = await seaport.getTokenBalance({
accountAddress, // string
tokenAddress: "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"
seaport 是 Opensea 的 JavaScript 電商程式建置套件，能夠作為 provider API 使用。
Weth 合約地址：
wETH 簡單來說就是與 ETH 錨定的同質化代幣，屬於 ERC-20 代幣的一種，也不能拿來支付 gas fee 等我們過往拿 ether 來使用的場景。wETH 好用的地方在於與 DeFi 產品互動，因為 DeFi 產品裡面都是同質化代幣與合約協議的互動，如果有一個 ether 一直卡在中間就會不斷的需要透過某個中介器去轉換（例如在合約裡面接收 msg.value 後，要有一個資料結構記住當前擁有者有多少的 ether 在合約裡面作用）。然而只要有了 wETH，用戶就可以直接使用 wETH 在 DeFi 合約裡面與其他代幣做無痛互動。當然 Dapps、DAOs 等也都會有相同問題，如果需要也可以在裡面使用 wETH 方便合約開發與運行。
可以看見主網上的 wETH 合約跟我們熟悉的 ERC-20 代幣標準運作過程如出一轍。
pragma solidity ^0.4.18;
contract WETH9 {
string public name = "Wrapped Ether";
string public symbol = "WETH";
uint8 public decimals = 18;
event Approval(address indexed src, address indexed guy, uint wad);
event Transfer(address indexed src, address indexed dst, uint wad);
event Deposit(address indexed dst, uint wad);
event Withdrawal(address indexed src, uint wad);
mapping (address => uint) public balanceOf;
mapping (address => mapping (address => uint)) public allowance;
function() public payable {
deposit();
}
function deposit() public payable {
balanceOf[msg.sender] += msg.value;
Deposit(msg.sender, msg.value);
}
function withdraw(uint wad) public {
require(balanceOf[msg.sender] >= wad);
balanceOf[msg.sender] -= wad;
msg.sender.transfer(wad);
Withdrawal(msg.sender, wad);
}
function totalSupply() public view returns (uint) {
return this.balance;
}
function approve(address guy, uint wad) public returns (bool) {
allowance[msg.sender][guy] = wad;
Approval(msg.sender, guy, wad);
return true;
}
function transfer(address dst, uint wad) public returns (bool) {
return transferFrom(msg.sender, dst, wad);
}
function transferFrom(address src, address dst, uint wad)
public
returns (bool)
{
require(balanceOf[src] >= wad);
if (src != msg.sender && allowance[src][msg.sender] != uint(-1)) {
require(allowance[src][msg.sender] >= wad);
allowance[src][msg.sender] -= wad;
}
balanceOf[src] -= wad;
balanceOf[dst] += wad;
Transfer(src, dst, wad);
return true;
}
}
在 Uniswap V1 中，我們其實沒辦法直接地互換 ERC-20 與 ERC-20 兩個代幣，而是 ERC20 to ERC20 swaps 會以 ETH 作為中介，下圖例子中如果我們要以 ABC 幣換 XYZ 幣，那就需要呼叫 ABC exchange Contract 中的 tokenToTokenSwap()，在經過一系列的 Check 和計算之後，這個 Function 會呼叫（internal call） XYZ exchange Contract 中的 payable function ethToTokenTransfer()。
ethToTokenTransfer() 在收到 Buyer Address 和 ETH 之後，一樣會經過計算和確認，最後利用 ERC20 的 transfer() 進行 Token 交易。
ethToTokenTransfer()比ethToTokenSwap()多了一個參數recipient: address，其他部分的作用一模一樣。因為我們沒辦法使用msg.sender來判斷 Buyer 是誰，在這裡當我們以 ABC Contract 去呼叫 XYZ Contract 時，msg.sender會是 ABC Contract Address 而不是 EOA Buyer。
@private
def tokenToTokenInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, buyer: address, recipient: address, exchange_addr: address) -> uint256:
assert (deadline >= block.timestamp and tokens_sold > 0) and (min_tokens_bought > 0 and min_eth_bought > 0)
assert exchange_addr != self and exchange_addr != ZERO_ADDRESS
token_reserve: uint256 = self.token.balanceOf(self)
eth_bought: uint256 = self.getInputPrice(tokens_sold, token_reserve, as_unitless_number(self.balance))
wei_bought: uint256(wei) = as_wei_value(eth_bought, 'wei')
assert wei_bought >= min_eth_bought
assert self.token.transferFrom(buyer, self, tokens_sold)
tokens_bought: uint256 = Exchange(exchange_addr).ethToTokenTransferInput(min_tokens_bought, deadline, recipient, value=wei_bought)
log.EthPurchase(buyer, tokens_sold, wei_bought)
return tokens_bought
# @notice Convert Tokens (self.token) to Tokens (token_addr).
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (token_addr) bought.
@public
def tokenToTokenSwapInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, token_addr: address) -> uint256:
exchange_addr: address = self.factory.getExchange(token_addr)
return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, msg.sender, exchange_addr)
# @notice Convert Tokens (self.token) to Tokens (token_addr) and transfers
# Tokens (token_addr) to recipient.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (token_addr) bought.
@public
def tokenToTokenTransferInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, recipient: address, token_addr: address) -> uint256:
exchange_addr: address = self.factory.getExchange(token_addr)
return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, recipient, exchange_addr)
@private
def tokenToTokenOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, buyer: address, recipient: address, exchange_addr: address) -> uint256:
assert deadline >= block.timestamp and (tokens_bought > 0 and max_eth_sold > 0)
assert exchange_addr != self and exchange_addr != ZERO_ADDRESS
eth_bought: uint256(wei) = Exchange(exchange_addr).getEthToTokenOutputPrice(tokens_bought)
token_reserve: uint256 = self.token.balanceOf(self)
tokens_sold: uint256 = self.getOutputPrice(as_unitless_number(eth_bought), token_reserve, as_unitless_number(self.balance))
# tokens sold is always > 0
assert max_tokens_sold >= tokens_sold and max_eth_sold >= eth_bought
assert self.token.transferFrom(buyer, self, tokens_sold)
eth_sold: uint256(wei) = Exchange(exchange_addr).ethToTokenTransferOutput(tokens_bought, deadline, recipient, value=eth_bought)
log.EthPurchase(buyer, tokens_sold, eth_bought)
return tokens_sold
# @notice Convert Tokens (self.token) to Tokens (token_addr).
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToTokenSwapOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, token_addr: address) -> uint256:
exchange_addr: address = self.factory.getExchange(token_addr)
return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, msg.sender, exchange_addr)
# @notice Convert Tokens (self.token) to Tokens (token_addr) and transfers
# Tokens (token_addr) to recipient.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToTokenTransferOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, recipient: address, token_addr: address) -> uint256:
exchange_addr: address = self.factory.getExchange(token_addr)
return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, recipient, exchange_addr)
# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token).
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (exchange_addr.token) bought.
@public
def tokenToExchangeSwapInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, exchange_addr: address) -> uint256:
return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, msg.sender, exchange_addr)
# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token) and transfers
# Tokens (exchange_addr.token) to recipient.
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies exact input and minimum output.
# @param tokens_sold Amount of Tokens sold.
# @param min_tokens_bought Minimum Tokens (token_addr) purchased.
# @param min_eth_bought Minimum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (exchange_addr.token) bought.
@public
def tokenToExchangeTransferInput(tokens_sold: uint256, min_tokens_bought: uint256, min_eth_bought: uint256(wei), deadline: timestamp, recipient: address, exchange_addr: address) -> uint256:
assert recipient != self
return self.tokenToTokenInput(tokens_sold, min_tokens_bought, min_eth_bought, deadline, msg.sender, recipient, exchange_addr)
# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token).
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param exchange_addr The address of the exchange for the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToExchangeSwapOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, exchange_addr: address) -> uint256:
return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, msg.sender, exchange_addr)
# @notice Convert Tokens (self.token) to Tokens (exchange_addr.token) and transfers
# Tokens (exchange_addr.token) to recipient.
# @dev Allows trades through contracts that were not deployed from the same factory.
# @dev User specifies maximum input and exact output.
# @param tokens_bought Amount of Tokens (token_addr) bought.
# @param max_tokens_sold Maximum Tokens (self.token) sold.
# @param max_eth_sold Maximum ETH purchased as intermediary.
# @param deadline Time after which this transaction can no longer be executed.
# @param recipient The address that receives output ETH.
# @param token_addr The address of the token being purchased.
# @return Amount of Tokens (self.token) sold.
@public
def tokenToExchangeTransferOutput(tokens_bought: uint256, max_tokens_sold: uint256, max_eth_sold: uint256(wei), deadline: timestamp, recipient: address, exchange_addr: address) -> uint256:
assert recipient != self
return self.tokenToTokenOutput(tokens_bought, max_tokens_sold, max_eth_sold, deadline, msg.sender, recipient, exchange_addr)
然而在 Uniswap V2 中 ETH 的角色都被改以 wETH 取代了，不管是什麼互換對都是使用 wETH。這邊引述 Uniswap/v2-core/contracts/UniswapV2Pair.sol 中 Swap 函式的部分。
V2 中 Pair 這個合約，是一個實作 swapping, minting, burning tokens 的合約，每一個 ERC-20 代幣交易對都會有一個 Pair Contract
// this low-level function should be called from a contract which performs important safety checks
function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external lock {
require(amount0Out > 0 || amount1Out > 0, 'UniswapV2: INSUFFICIENT_OUTPUT_AMOUNT');
(uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
require(amount0Out < _reserve0 && amount1Out < _reserve1, 'UniswapV2: INSUFFICIENT_LIQUIDITY');
uint balance0;
uint balance1;
{ // scope for _token{0,1}, avoids stack too deep errors
address _token0 = token0;
address _token1 = token1;
require(to != _token0 && to != _token1, 'UniswapV2: INVALID_TO');
if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
if (data.length > 0) IUniswapV2Callee(to).uniswapV2Call(msg.sender, amount0Out, amount1Out, data);
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
}
uint amount0In = balance0 > _reserve0 - amount0Out ? balance0 - (_reserve0 - amount0Out) : 0;
uint amount1In = balance1 > _reserve1 - amount1Out ? balance1 - (_reserve1 - amount1Out) : 0;
require(amount0In > 0 || amount1In > 0, 'UniswapV2: INSUFFICIENT_INPUT_AMOUNT');
{ // scope for reserve{0,1}Adjusted, avoids stack too deep errors
uint balance0Adjusted = balance0.mul(1000).sub(amount0In.mul(3));
uint balance1Adjusted = balance1.mul(1000).sub(amount1In.mul(3));
require(balance0Adjusted.mul(balance1Adjusted) >= uint(_reserve0).mul(_reserve1).mul(1000**2), 'UniswapV2: K');
}
_update(balance0, balance1, _reserve0, _reserve1);
emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
}
最後歡迎大家拍打餵食大學生
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