《纸上谈兵·solidity》第 42 课：DeFi 实战(6) -- 跨资产借贷与多市场支持
1. 学习目标
- 理解为什么借贷协议必须支持多种资产而不是单一代币。
- 掌握市场（Market）的概念：每个资产拥有独立的借贷池、利率模型、抵押参数。
- 学习 跨资产借贷 的关键逻辑：抵押物与借款资产之间的价值评估。
- 实现一个多市场借贷平台原型，允许用户用 A 代币抵押，借出 B 代币。
2. 背景与概念
2.1 为什么需要多资产支持？
单资产借贷（例如只能抵押 ETH 借出 ETH）意义不大。现实需求是：
- 用户抵押 稳定资产（如 USDC、stETH） → 借出 高风险资产（如 WETH、WBTC） 做投资。
- 用户抵押 波动性资产（如 ETH） → 借出 稳定币 进行流动性操作或现实消费。
- 借贷平台的 TVL（总锁仓量）越多，吸引力越大，而 TVL 的来源就是多样化资产的引入。
2.2 市场（Market）的抽象
在 Compound/Aave 里，每个资产都有一个独立的市场：
- 独立的资金池（Cash、Borrow、Reserves）。
- 独立的利率曲线（基于 Utilization 计算）。
- 独立的参数（抵押因子、清算阈值、储备金比例）。
用户视角：
- 我可以存 USDC → 得到利息（变成 aUSDC）。
- 我可以存 ETH → 抵押借出 USDC。
- 每个市场单独计息，但用户的整体借贷头寸由价格预言机整合评估。
2.3 跨资产借贷
跨资产借贷的本质是：
- 用户抵押资产
C（Collateral）。 - 用户想借出资产
B（Borrow）。 - 协议需要比较 抵押物价值 与 借款价值。
公式：
Collateral Value × Collateral Factor ≥ Borrow Value其中：
Collateral Value通过 预言机价格 × 抵押数量 计算。Collateral Factor是风险折扣（如 ETH = 75%，USDC = 90%）。Borrow Value同样由预言机计算。
3. 合约设计思路
我们将扩展之前的 LendingPool，加入 Market 管理：
struct MarketIERC20 token→ 市场的资产。uint256 collateralFactor→ 抵押因子。uint256 totalDepositsuint256 totalBorrowsmapping(address => mapping(address => uint256)) userDepositsmapping(address => mapping(address => uint256)) userBorrows
这里第一层 address 表示市场资产，第二层表示用户。
4. 核心合约示例
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
/**
* @title Price Oracle Interface
* @notice Provides price data for tokens
*/
interface IPriceOracle {
/**
* @notice Get the price of a token
* @param token The token address to get price for
* @return The price of the token, scaled by 1e18
*/
function getPrice(address token) external view returns (uint256);
}
/**
* @title MultiMarketLending
* @notice A multi-market lending protocol supporting multiple collateral assets
* @dev This contract allows users to deposit collateral and borrow against it across multiple markets
*/
contract MultiMarketLending is ReentrancyGuard {
/**
* @notice Market configuration structure
* @dev Collateral factor is scaled by FACTOR_BASE (10000 = 100%)
*/
struct Market {
IERC20 token; // The ERC20 token for this market
uint256 collateralFactor; // Collateral factor scaled by FACTOR_BASE
uint256 totalDeposits; // Total amount deposited in this market
uint256 totalBorrows; // Total amount borrowed from this market
bool isListed; // Whether this market is active
}
/// @notice Mapping from token address to market configuration
mapping(address => Market) public markets;
/// @notice Mapping from (token, user) to deposit amount
mapping(address => mapping(address => uint256)) public userDeposits;
/// @notice Mapping from (token, user) to borrow amount
mapping(address => mapping(address => uint256)) public userBorrows;
/// @notice Mapping from user to list of tokens they have deposited as collateral
mapping(address => address[]) public userCollateralTokens;
/// @notice Mapping from user to list of tokens they have borrowed
mapping(address => address[]) public userBorrowTokens;
/// @notice The price oracle contract used for price feeds
IPriceOracle public oracle;
/// @notice Base value for collateral factor calculations (10000 = 100%)
uint256 public constant FACTOR_BASE = 10000;
/**
* @notice Contract constructor
* @param _oracle The address of the price oracle contract
*/
constructor(address _oracle) {
oracle = IPriceOracle(_oracle);
}
/**
* @notice Add a new market to the protocol
* @dev Only callable by anyone in this implementation (consider adding access control)
* @param token The ERC20 token address for the new market
* @param collateralFactor The collateral factor for this market (scaled by FACTOR_BASE)
*/
function addMarket(address token, uint256 collateralFactor) external {
require(!markets[token].isListed, "already exists");
markets[token] = Market({
token: IERC20(token),
collateralFactor: collateralFactor,
totalDeposits: 0,
totalBorrows: 0,
isListed: true
});
}
/**
* @notice Deposit tokens as collateral
* @dev Uses nonReentrant modifier to prevent reentrancy attacks
* @param token The token address to deposit
* @param amount The amount of tokens to deposit
*/
function deposit(address token, uint256 amount) external nonReentrant {
Market storage m = markets[token];
require(m.isListed, "market not exist");
// Transfer tokens from user to contract
m.token.transferFrom(msg.sender, address(this), amount);
// If this is user's first deposit of this token, add to collateral list
if (userDeposits[token][msg.sender] == 0) {
userCollateralTokens[msg.sender].push(token);
}
// Update user deposit and market totals
userDeposits[token][msg.sender] += amount;
m.totalDeposits += amount;
}
/**
* @notice Borrow tokens against collateral
* @dev Uses nonReentrant modifier to prevent reentrancy attacks
* @param token The token address to borrow
* @param amount The amount of tokens to borrow
*/
function borrow(address token, uint256 amount) external nonReentrant {
Market storage m = markets[token];
require(m.isListed, "market not exist");
// Check if user has sufficient collateral to borrow
require(
_canBorrow(msg.sender, token, amount),
"insufficient collateral"
);
// If this is user's first borrow of this token, add to borrow list
if (userBorrows[token][msg.sender] == 0) {
userBorrowTokens[msg.sender].push(token);
}
// Update market and user borrow amounts
m.totalBorrows += amount;
userBorrows[token][msg.sender] += amount;
// Transfer borrowed tokens to user
m.token.transfer(msg.sender, amount);
}
/**
* @notice Internal function to check if a user can borrow specified amount
* @dev Calculates total collateral value and compares with existing + new borrow value
* @param user The address of the user
* @param borrowToken The token the user wants to borrow
* @param amount The amount the user wants to borrow
* @return True if user can borrow, false otherwise
*/
function _canBorrow(
address user,
address borrowToken,
uint256 amount
) internal view returns (bool) {
// Calculate the value of the requested borrow
uint256 borrowValue = (oracle.getPrice(borrowToken) * amount) / 1e18;
uint256 totalCollateralValue = 0;
// Calculate total collateral value from all deposited tokens
address[] memory tokens = userCollateralTokens[user];
for (uint256 i = 0; i < tokens.length; i++) {
address token = tokens[i];
uint256 depositAmount = userDeposits[token][user];
if (depositAmount == 0) continue;
uint256 price = oracle.getPrice(token);
// Apply collateral factor to get borrowable value
uint256 value = (((depositAmount * price) / 1e18) *
markets[token].collateralFactor) / FACTOR_BASE;
totalCollateralValue += value;
}
// Calculate current borrow value from all borrowed tokens
uint256 currentBorrowValue = 0;
address[] memory borrowTokens = userBorrowTokens[user];
for (uint256 i = 0; i < borrowTokens.length; i++) {
address token = borrowTokens[i];
uint256 borrowAmt = userBorrows[token][user];
if (borrowAmt == 0) continue;
uint256 price = oracle.getPrice(token);
currentBorrowValue += (borrowAmt * price) / 1e18;
}
// Check if collateral covers existing + new borrows
return totalCollateralValue >= currentBorrowValue + borrowValue;
}
}5. 测试场景
MultiMarketLending.t.sol：
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;
import "forge-std/Test.sol";
import "../src/MultiMarketLending.sol";
/**
* @title Mock ERC20 Token
* @notice Mock implementation of ERC20 for testing purposes
* @dev Simulates ERC20 token behavior without external dependencies
*/
contract MockERC20 is IERC20 {
string public name;
string public symbol;
uint8 public decimals = 18;
uint256 public override totalSupply;
mapping(address => uint256) public override balanceOf;
mapping(address => mapping(address => uint256)) public override allowance;
/**
* @notice Initialize mock token with name and symbol
* @param _name Token name
* @param _symbol Token symbol
*/
constructor(string memory _name, string memory _symbol) {
name = _name;
symbol = _symbol;
}
/**
* @notice Transfer tokens to a specified address
* @param to The address to transfer to
* @param amount The amount to transfer
* @return success Whether the transfer was successful
*/
function transfer(
address to,
uint256 amount
) external override returns (bool) {
require(balanceOf[msg.sender] >= amount, "insufficient");
balanceOf[msg.sender] -= amount;
balanceOf[to] += amount;
emit Transfer(msg.sender, to, amount);
return true;
}
/**
* @notice Approve spender to transfer tokens on behalf of msg.sender
* @param spender The address allowed to spend
* @param amount The amount allowed to spend
* @return success Whether the approval was successful
*/
function approve(
address spender,
uint256 amount
) external override returns (bool) {
allowance[msg.sender][spender] = amount;
emit Approval(msg.sender, spender, amount);
return true;
}
/**
* @notice Transfer tokens from one address to another using allowance
* @param from The address to transfer from
* @param to The address to transfer to
* @param amount The amount to transfer
* @return success Whether the transfer was successful
*/
function transferFrom(
address from,
address to,
uint256 amount
) external override returns (bool) {
require(balanceOf[from] >= amount, "insufficient");
require(allowance[from][msg.sender] >= amount, "no allowance");
allowance[from][msg.sender] -= amount;
balanceOf[from] -= amount;
balanceOf[to] += amount;
emit Transfer(from, to, amount);
return true;
}
/**
* @notice Mint new tokens to specified address
* @dev Only for testing - creates tokens out of thin air
* @param to The address to receive minted tokens
* @param amount The amount to mint
*/
function mint(address to, uint256 amount) external {
balanceOf[to] += amount;
totalSupply += amount;
emit Transfer(address(0), to, amount);
}
}
/**
* @title Mock Price Oracle
* @notice Mock implementation of price oracle for testing
* @dev Allows setting arbitrary prices for testing different scenarios
*/
contract MockOracle is IPriceOracle {
/// @notice Mapping from token address to price
mapping(address => uint256) public prices;
/**
* @notice Set price for a token
* @param token The token address
* @param price The price to set (scaled by 1e18)
*/
function setPrice(address token, uint256 price) external {
prices[token] = price;
}
/**
* @notice Get price for a token
* @param token The token address
* @return The current price of the token (scaled by 1e18)
*/
function getPrice(address token) external view override returns (uint256) {
return prices[token];
}
}
/**
* @title MultiMarketLending Test Suite
* @notice Comprehensive test suite for MultiMarketLending contract
* @dev Uses Foundry testing framework with cheat codes
*/
contract MultiMarketLendingTest is Test {
/// @notice The lending contract being tested
MultiMarketLending lending;
/// @notice Mock ETH token for testing
MockERC20 ethToken;
/// @notice Mock USDC token for testing
MockERC20 usdcToken;
/// @notice Mock price oracle for testing
MockOracle oracle;
/// @notice Test user address 1
address user1 = address(0x123);
/// @notice Test user address 2
address user2 = address(0x234);
/**
* @notice Set up test environment before each test
* @dev Deploys contracts, sets up markets, and initializes test data
*/
function setUp() public {
oracle = new MockOracle();
lending = new MultiMarketLending(address(oracle));
ethToken = new MockERC20("Mock ETH", "mETH");
usdcToken = new MockERC20("Mock USDC", "mUSDC");
// Set prices: ETH = $2000, USDC = $1
oracle.setPrice(address(ethToken), 2000 ether);
oracle.setPrice(address(usdcToken), 1 ether);
// Add markets with collateral factors
lending.addMarket(address(ethToken), 7500); // ETH collateral factor = 75%
lending.addMarket(address(usdcToken), 9000); // USDC collateral factor = 90%
// Mint tokens to users and contract
ethToken.mint(user1, 10 ether);
usdcToken.mint(address(lending), 10_000 ether); // Provide liquidity to pool
}
/**
* @notice Test basic deposit functionality
* @dev Verifies that users can deposit tokens and balances are updated correctly
*/
function test_Deposit() public {
vm.startPrank(user1);
ethToken.approve(address(lending), 1 ether);
lending.deposit(address(ethToken), 1 ether);
vm.stopPrank();
assertEq(lending.userDeposits(address(ethToken), user1), 1 ether);
}
/**
* @notice Test borrowing within collateral limits
* @dev Verifies users can borrow up to their collateral limit
*/
function test_Borrow_WithinLimit() public {
vm.startPrank(user1);
// Deposit 1 ETH as collateral
ethToken.approve(address(lending), 1 ether);
lending.deposit(address(ethToken), 1 ether);
// Borrow up to limit: $2000 * 75% = $1500 USDC
lending.borrow(address(usdcToken), 1500 ether);
vm.stopPrank();
assertEq(lending.userBorrows(address(usdcToken), user1), 1500 ether);
assertEq(usdcToken.balanceOf(user1), 1500 ether);
}
/**
* @notice Test borrowing beyond collateral limits reverts
* @dev Verifies that borrowing beyond collateral limits fails as expected
*/
function test_RevertWhen_Borrow_ExceedLimit() public {
vm.startPrank(user1);
ethToken.approve(address(lending), 1 ether);
lending.deposit(address(ethToken), 1 ether);
// Attempt to borrow $2000 USDC (exceeds $1500 limit)
vm.expectRevert();
lending.borrow(address(usdcToken), 2000 ether);
vm.stopPrank();
}
/**
* @notice Test multiple users have independent accounts
* @dev Verifies that user positions don't interfere with each other
*/
function test_MultipleUsers_Independent() public {
vm.startPrank(user1);
ethToken.approve(address(lending), 1 ether);
lending.deposit(address(ethToken), 1 ether);
lending.borrow(address(usdcToken), 1000 ether);
vm.stopPrank();
vm.startPrank(user2);
ethToken.mint(user2, 2 ether);
ethToken.approve(address(lending), 2 ether);
lending.deposit(address(ethToken), 2 ether);
lending.borrow(address(usdcToken), 2000 ether);
vm.stopPrank();
assertEq(lending.userBorrows(address(usdcToken), user1), 1000 ether);
assertEq(lending.userBorrows(address(usdcToken), user2), 2000 ether);
}
/**
* @notice Test sequential borrowing with limit enforcement
* @dev Verifies that second borrow attempt respects cumulative borrowing
*/
function test_When_BorrowSecondTime_ExceedsLimit() public {
vm.startPrank(user1);
ethToken.approve(address(lending), 1 ether);
lending.deposit(address(ethToken), 1 ether);
// First borrow: 1000 USDC
lending.borrow(address(usdcToken), 1000 ether);
// Second borrow: 600 USDC, total = 1600 > 1500 limit
vm.expectRevert();
lending.borrow(address(usdcToken), 600 ether);
vm.stopPrank();
}
/**
* @notice Test operations on non-existent markets revert
* @dev Verifies proper error handling for invalid market operations
*/
function test_RevertWhen_NonExistentMarket() public {
MockERC20 fake = new MockERC20("Fake", "FAKE");
vm.startPrank(user1);
fake.mint(user1, 100 ether);
fake.approve(address(lending), 100 ether);
vm.expectRevert("market not exist");
lending.deposit(address(fake), 100 ether);
vm.stopPrank();
}
/**
* @notice Test borrowing with multiple collateral types
* @dev Verifies collateral value calculation across multiple asset types
*/
function test_RevertWhen_MultiCollateralBorrow() public {
vm.startPrank(user1);
// Deposit 1 ETH ($2000, 75%) + 1000 USDC ($1000, 90%)
ethToken.approve(address(lending), 1 ether);
lending.deposit(address(ethToken), 1 ether);
usdcToken.mint(user1, 1000 ether);
usdcToken.approve(address(lending), 1000 ether);
lending.deposit(address(usdcToken), 1000 ether);
// Total collateral value = 2000*0.75 + 1000*0.9 = 1500 + 900 = $2400
// Borrow 2000 USDC should succeed
lending.borrow(address(usdcToken), 2000 ether);
// Borrow additional 500 USDC should fail (2400 < 2500)
vm.expectRevert();
lending.borrow(address(usdcToken), 500 ether);
vm.stopPrank();
}
}执行测试：
➜ defi git:(master) ✗ forge test --match-path test/MultiMarketLending.t.sol -vvv
[⠊] Compiling...
[⠒] Compiling 1 files with Solc 0.8.29
[⠑] Solc 0.8.29 finished in 1.50s
Compiler run successful!
Ran 7 tests for test/MultiMarketLending.t.sol:MultiMarketLendingTest
[PASS] test_Borrow_WithinLimit() (gas: 305862)
[PASS] test_Deposit() (gas: 154597)
[PASS] test_MultipleUsers_Independent() (gas: 507254)
[PASS] test_RevertWhen_Borrow_ExceedLimit() (gas: 181121)
[PASS] test_RevertWhen_MultiCollateralBorrow() (gas: 418155)
[PASS] test_RevertWhen_NonExistentMarket() (gas: 933374)
[PASS] test_When_BorrowSecondTime_ExceedsLimit() (gas: 317027)
Suite result: ok. 7 passed; 0 failed; 0 skipped; finished in 1.74ms (2.83ms CPU time)
Ran 1 test suite in 429.38ms (1.74ms CPU time): 7 tests passed, 0 failed, 0 skipped (7 total tests)6. 总结
本课重点：
- 借贷平台真正的价值在于 多资产 + 跨市场。
- 每个资产市场独立存在，但通过价格预言机和抵押因子实现统一的风险控制。
- 跨资产借贷的核心是 抵押价值 ≥ 借款价值。
- 为简化课程，我们先实现框架，后续课程可逐步扩展清算、利率模型、治理参数。
7. 作业
- 补充一个 多资产借贷（抵押 ETH 借 USDC + WBTC） 的测试
- 思考：
- 为什么 USDC 的抵押因子（90%）高于 ETH（75%）？
- 在真实协议中，哪些资产会有更低的抵押因子？
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