從 Solidity 智能合約轉帳與授權 ERC-20 代幣
智能合約
代幣
Solidity
erc-20
中階
在上一篇教學中，我們學習了以太坊區塊鏈上 Solidity 中 ERC-20 代幣的剖析。在本文中，我們將了解如何使用 Solidity 語言透過智能合約與代幣進行互動。
針對這個智能合約，我們將建立一個真正的模擬去中心化交易所 (DEX)，使用者可以在其中用以太幣兌換我們新部署的 ERC-20 代幣。
在本教學中，我們將以在上一篇教學中編寫的程式碼為基礎。我們的 DEX 將在其建構函式中實例化該合約的實例，並執行以下操作：
- 將代幣兌換為以太幣
- 將以太幣兌換為代幣
我們將透過加入簡單的 ERC20 程式碼庫來開始編寫去中心化交易所程式碼：
pragma solidity ^0.8.0;
interface IERC20 {
function totalSupply() external view returns (uint256);
function balanceOf(address account) external view returns (uint256);
function allowance(address owner, address spender) external view returns (uint256);
function transfer(address recipient, uint256 amount) external returns (bool);
function approve(address spender, uint256 amount) external returns (bool);
function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
event Transfer(address indexed from, address indexed to, uint256 value);
event Approval(address indexed owner, address indexed spender, uint256 value);
}
contract ERC20Basic is IERC20 {
string public constant name = "ERC20Basic";
string public constant symbol = "ERC";
uint8 public constant decimals = 18;
mapping(address => uint256) balances;
mapping(address => mapping (address => uint256)) allowed;
uint256 totalSupply_ = 10 ether;
constructor() {
balances[msg.sender] = totalSupply_;
}
function totalSupply() public override view returns (uint256) {
return totalSupply_;
}
function balanceOf(address tokenOwner) public override view returns (uint256) {
return balances[tokenOwner];
}
function transfer(address receiver, uint256 numTokens) public override returns (bool) {
require(numTokens <= balances[msg.sender]);
balances[msg.sender] = balances[msg.sender]-numTokens;
balances[receiver] = balances[receiver]+numTokens;
emit Transfer(msg.sender, receiver, numTokens);
return true;
}
function approve(address delegate, uint256 numTokens) public override returns (bool) {
allowed[msg.sender][delegate] = numTokens;
emit Approval(msg.sender, delegate, numTokens);
return true;
}
function allowance(address owner, address delegate) public override view returns (uint) {
return allowed[owner][delegate];
}
function transferFrom(address owner, address buyer, uint256 numTokens) public override returns (bool) {
require(numTokens <= balances[owner]);
require(numTokens <= allowed[owner][msg.sender]);
balances[owner] = balances[owner]-numTokens;
allowed[owner][msg.sender] = allowed[owner][msg.sender]-numTokens;
balances[buyer] = balances[buyer]+numTokens;
emit Transfer(owner, buyer, numTokens);
return true;
}
}
我們新的 DEX 智能合約將部署 ERC-20 並取得所有供應量：
contract DEX {
IERC20 public token;
event Bought(uint256 amount);
event Sold(uint256 amount);
constructor() {
token = new ERC20Basic();
}
function buy() payable public {
// TODO
}
function sell(uint256 amount) public {
// TODO
}
}
現在我們有了 DEX，並且它擁有所有可用的代幣儲備。該合約有兩個函式：
buy：使用者可以發送以太幣並換取等值的代幣sell：使用者可以決定發送代幣以換回以太幣
購買函式
讓我們來編寫購買函式。我們首先需要檢查訊息中包含的以太幣數量，並驗證合約擁有足夠的代幣，且訊息中確實包含一些以太幣。如果合約擁有足夠的代幣，它會將相應數量的代幣發送給使用者，並觸發 Bought 事件。
請注意，如果在發生錯誤的情況下呼叫 require 函式，發送的以太幣將直接被還原並退還給使用者。
為了保持簡單，我們只以 1 個代幣兌換 1 Wei。
function buy() payable public {
uint256 amountTobuy = msg.value;
uint256 dexBalance = token.balanceOf(address(this));
require(amountTobuy > 0, "You need to send some ether");
require(amountTobuy <= dexBalance, "Not enough tokens in the reserve");
token.transfer(msg.sender, amountTobuy);
emit Bought(amountTobuy);
}
在購買成功的情況下，我們應該會在交易中看到兩個事件：代幣的 Transfer 事件和 Bought 事件。
出售函式
負責出售的函式首先會要求使用者事先呼叫 approve 函式來授權該數量。授權轉帳需要使用者呼叫由 DEX 實例化的 ERC20Basic 代幣。這可以透過首先呼叫 DEX 合約的 token() 函式來實現，以取得 DEX 部署名為 token 的 ERC20Basic 合約的地址。然後，我們在工作階段中建立該合約的實例並呼叫其 approve 函式。接著，我們就能夠呼叫 DEX 的 sell 函式，並將我們的代幣兌換回以太幣。例如，這在互動式 Brownie 工作階段中的樣子如下：
#### 在互動式 Brownie 控制台中的 Python...
# 部署 DEX
dex = DEX.deploy({'from':account1})
# 呼叫 buy 函式以將以太幣兌換為代幣
# 1e18 是以 Wei 為單位的 1 以太幣
dex.buy({'from': account2, 1e18})
# 取得 ERC20 代幣的部署地址
# 這是在 DEX 合約建立期間部署的
# dex.token() 會回傳代幣的部署地址
token = ERC20Basic.at(dex.token())
# 呼叫代幣的授權函式
# 授權 dex 地址作為花費者
# 以及允許它花費多少你的代幣
token.approve(dex.address, 3e18, {'from':account2})
然後，當呼叫出售函式時，我們將檢查從呼叫者地址到合約地址的轉帳是否成功，然後將以太幣發送回呼叫者地址。
function sell(uint256 amount) public {
require(amount > 0, "You need to sell at least some tokens");
uint256 allowance = token.allowance(msg.sender, address(this));
require(allowance >= amount, "Check the token allowance");
token.transferFrom(msg.sender, address(this), amount);
payable(msg.sender).transfer(amount);
emit Sold(amount);
}
如果一切正常，您應該會在交易中看到 2 個事件（一個 Transfer 和一個 Sold），並且您的代幣餘額和以太幣餘額已更新。
透過本教學，我們了解了如何檢查 ERC-20 代幣的餘額和授權額度，以及如何使用介面呼叫 ERC20 智能合約的 Transfer 和 TransferFrom。
一旦您進行了交易，我們有一個 JavaScript 教學可以等待並取得對您合約進行的交易詳細資訊 (opens in a new tab)，以及一個教學來解碼由代幣轉帳或任何其他事件產生的事件 (opens in a new tab)（只要您有 ABI）。
以下是本教學的完整程式碼：
pragma solidity ^0.8.0;
interface IERC20 {
function totalSupply() external view returns (uint256);
function balanceOf(address account) external view returns (uint256);
function allowance(address owner, address spender) external view returns (uint256);
function transfer(address recipient, uint256 amount) external returns (bool);
function approve(address spender, uint256 amount) external returns (bool);
function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
event Transfer(address indexed from, address indexed to, uint256 value);
event Approval(address indexed owner, address indexed spender, uint256 value);
}
contract ERC20Basic is IERC20 {
string public constant name = "ERC20Basic";
string public constant symbol = "ERC";
uint8 public constant decimals = 18;
mapping(address => uint256) balances;
mapping(address => mapping (address => uint256)) allowed;
uint256 totalSupply_ = 10 ether;
constructor() {
balances[msg.sender] = totalSupply_;
}
function totalSupply() public override view returns (uint256) {
return totalSupply_;
}
function balanceOf(address tokenOwner) public override view returns (uint256) {
return balances[tokenOwner];
}
function transfer(address receiver, uint256 numTokens) public override returns (bool) {
require(numTokens <= balances[msg.sender]);
balances[msg.sender] = balances[msg.sender]-numTokens;
balances[receiver] = balances[receiver]+numTokens;
emit Transfer(msg.sender, receiver, numTokens);
return true;
}
function approve(address delegate, uint256 numTokens) public override returns (bool) {
allowed[msg.sender][delegate] = numTokens;
emit Approval(msg.sender, delegate, numTokens);
return true;
}
function allowance(address owner, address delegate) public override view returns (uint) {
return allowed[owner][delegate];
}
function transferFrom(address owner, address buyer, uint256 numTokens) public override returns (bool) {
require(numTokens <= balances[owner]);
require(numTokens <= allowed[owner][msg.sender]);
balances[owner] = balances[owner]-numTokens;
allowed[owner][msg.sender] = allowed[owner][msg.sender]-numTokens;
balances[buyer] = balances[buyer]+numTokens;
emit Transfer(owner, buyer, numTokens);
return true;
}
}
contract DEX {
event Bought(uint256 amount);
event Sold(uint256 amount);
IERC20 public token;
constructor() {
token = new ERC20Basic();
}
function buy() payable public {
uint256 amountTobuy = msg.value;
uint256 dexBalance = token.balanceOf(address(this));
require(amountTobuy > 0, "You need to send some ether");
require(amountTobuy <= dexBalance, "Not enough tokens in the reserve");
token.transfer(msg.sender, amountTobuy);
emit Bought(amountTobuy);
}
function sell(uint256 amount) public {
require(amount > 0, "You need to sell at least some tokens");
uint256 allowance = token.allowance(msg.sender, address(this));
require(allowance >= amount, "Check the token allowance");
token.transferFrom(msg.sender, address(this), amount);
payable(msg.sender).transfer(amount);
emit Sold(amount);
}
}