从 Solidity 智能合约转账和授权 ERC-20 代币
智能合约
代币
Solidity
erc-20
中级
在上一篇教程中，我们学习了以太坊区块链上 Solidity 中 ERC-20 代币的剖析。在本文中，我们将了解如何使用 Solidity 语言通过智能合约与代币进行交互。
对于这个智能合约，我们将创建一个真正的虚拟去中心化交易所 (DEX)，用户可以在其中用以太币兑换我们新部署的 ERC-20 代币。
在本教程中，我们将使用在上一篇教程中编写的代码作为基础。我们的 DEX 将在其构造函数中实例化该合约的一个实例，并执行以下操作：
- 将代币兑换为以太币
- 将以太币兑换为代币
我们将通过添加简单的 ERC-20 代码库来开始编写去中心化交易所代码：
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;
}
}
我们新的 DEX 智能合约将部署 ERC-20 并获取所有供应量：
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
}
}
现在我们有了 DEX，并且它拥有所有可用的代币储备。该合约有两个函数：
buy：用户可以发送以太币并兑换获得代币sell：用户可以决定发送代币以换回以太币
buy（购买）函数
让我们编写 buy 函数。我们首先需要检查消息中包含的以太币数量，并验证合约是否拥有足够的代币，以及消息中是否包含一些以太币。如果合约拥有足够的代币，它将向用户发送相应数量的代币并触发 Bought 事件。
请注意，如果在发生错误时调用 require 函数，发送的以太币将被直接回滚并退还给用户。
为了保持简单，我们只按 1 个代币兑换 1 Wei 的比例进行兑换。
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);
}
在购买成功的情况下，我们应该在交易中看到两个事件：代币的 Transfer 事件和 Bought 事件。
sell（出售）函数
负责出售的函数首先会要求用户事先调用 approve 函数来授权该金额。授权转账需要用户调用由 DEX 实例化的 ERC20Basic 代币。这可以通过首先调用 DEX 合约的 token() 函数来检索 DEX 部署名为 token 的 ERC20Basic 合约的地址来实现。然后，我们在会话中创建该合约的实例并调用其 approve 函数。接着，我们就可以调用 DEX 的 sell 函数并将我们的代币兑换回以太币。例如，在交互式 Brownie 会话中，它的过程如下所示：
#### 交互式 Brownie 控制台中的 Python...
# 部署 DEX
dex = DEX.deploy({'from':account1})
# 调用 buy 函数将以太币兑换为代币
# 1e18 是以 Wei 为单位的 1 个以太币
dex.buy({'from': account2, 1e18})
# 获取 ERC-20 代币的部署地址
# 它是在 DEX 合约创建期间部署的
# dex.token() 返回代币的部署地址
token = ERC20Basic.at(dex.token())
# 调用代币的授权函数
# 授权 dex 地址作为支出方
# 以及允许它花费你的多少代币
token.approve(dex.address, 3e18, {'from':account2})
然后，当调用 sell 函数时，我们将检查从调用者地址到合约地址的转账是否成功，然后将以太币发送回调用者地址。
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，你应该会在交易中看到 2 个事件（一个 Transfer 和一个 Sold），并且你的代币余额和以太币余额也会更新。
通过本教程，我们了解了如何检查 ERC-20 代币的余额和授权额度，以及如何使用接口调用 ERC-20 智能合约的 Transfer 和 TransferFrom。
一旦你进行了一笔交易，我们有一个 JavaScript 教程来教你如何等待并获取有关向你的合约发起的交易的详细信息 (opens in a new tab)，以及一个教程来解码由代币转账或任何其他事件生成的事件 (opens in a new tab)（只要你有 ABI）。
以下是本教程的完整代码：
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);
}
}