curve-integration

# Curve Finance Integration ## Pool Types | Pool Type | Use Case | Math | |-----------|----------|------| | StableSwap | Pegged assets (USDC/USDT/DAI) | Hybrid constant-sum/constant-product | | CryptoSwap | Volatile pairs (ETH/CRV) | Dynamic peg with internal oracle | | Meta-pool | Pairs against 3pool LP (fraxBP) | Nested pool composition | | Tricrypto | Three volatile assets | Generalized crypto invariant | ## StableSwap Amplification Parameter (A) The invariant is a blend of constant-sum (A = infinity) and constant-product (A = 0): ``` A * n^n * sum(x_i) + D = A * D * n^n + D^(n+1) / (n^n * prod(x_i)) ``` - Higher A: tighter peg, lower slippage near peg, catastrophic slippage far from peg - Lower A: behaves more like Uniswap constant-product - Typical A: 100-2000 for stablecoin pools ## Core Swap Interface ```solidity interface ICurvePool { // Exchange tokens within the pool // i = input token index, j = output token index function exchange(int128 i, int128 j, uint256 dx, uint256 min_dy) external returns (uint256); // For ETH pools, send ETH as msg.value function exchange(int128 i, int128 j, uint256 dx, uint256 min_dy) external payable returns (uint256); // Get expected output (use for quoting, NOT as min_dy) function get_dy(int128 i, int128 j, uint256 dx) external view returns (uint256); // Liquidity operations function add_liquidity(uint256[3] calldata amounts, uint256 min_mint_amount) external returns (uint256); function remove_liquidity(uint256 _amount, uint256[3] calldata min_amounts) external returns (uint256[3] memory); function remove_liquidity_one_coin(uint256 _amount, int128 i, uint256 min_amount) external returns (uint256); function get_virtual_price() external view returns (uint256); function A() external view returns (uint256); function balances(uint256 i) external view returns (uint256); } ``` ## Safe Swap Pattern ```solidity contract CurveSwapper { ICurvePool public immutable pool; uint256 public constant MAX_SLIPPAGE_BPS = 50; // 0.5% constructor(address _pool) { pool = ICurvePool(_pool); } function swap( int128 tokenIn, int128 tokenOut, uint256 amountIn, address recipient ) external returns (uint256 amountOut) { IERC20(pool.coins(uint256(int256(tokenIn)))).transferFrom( msg.sender, address(this), amountIn ); IERC20(pool.coins(uint256(int256(tokenIn)))).approve(address(pool), amountIn); uint256 expected = pool.get_dy(tokenIn, tokenOut, amountIn); uint256 minOut = expected * (10000 - MAX_SLIPPAGE_BPS) / 10000; amountOut = pool.exchange(tokenIn, tokenOut, amountIn, minOut); IERC20(pool.coins(uint256(int256(tokenOut)))).transfer(recipient, amountOut); } } ``` ## stETH/ETH Pool Integration ```solidity // Curve stETH/ETH pool: 0xDC24316b9AE028F1497c275EB9192a3Ea0f67022 // Index 0 = ETH, Index 1 = stETH ICurvePool stethPool = ICurvePool(0xDC24316b9AE028F1497c275EB9192a3Ea0f67022); // Swap ETH -> stETH uint256 minSteth = stethPool.get_dy(0, 1, msg.value) * 9950 / 10000; uint256 received = stethPool.exchange{value: msg.value}(0, 1, msg.value, minSteth); // Swap stETH -> ETH IERC20(steth).approve(address(stethPool), amount); uint256 ethReceived = stethPool.exchange(1, 0, amount, minEth); ``` ## Gauge Voting and CRV Rewards ```solidity interface ICurveGauge { function deposit(uint256 _value) external; function withdraw(uint256 _value) external; function claim_rewards() external; function claimable_reward(address _addr, address _token) external view returns (uint256); function balanceOf(address) external view returns (uint256); } // Deposit LP tokens into gauge to earn CRV IERC20(lpToken).approve(address(gauge), amount); gauge.deposit(amount); // Claim CRV rewards gauge.claim_rewards(); ``` ## Virtual Price and LP Valuation `get_virtual_price()` returns the value of 1 LP token in terms of the pool's unit of account. It should only increase (manipulation-resistant). ```solidity // LP value = lp_balance * virtual_price / 1e18 uint256 virtualPrice = pool.get_virtual_price(); uint256 lpValue = lpBalance * virtualPrice / 1e18; ``` **Warning**: Do NOT use `get_virtual_price()` as a price oracle for lending — it was exploitable via read-only reentrancy in older Vyper versions. Use Chainlink or Curve's dedicated oracle for that purpose. ## Checklist - [ ] Use `get_dy()` for quoting but apply your own slippage tolerance for `min_dy` - [ ] Handle ETH pools via `msg.value` (index 0 is typically native ETH) - [ ] Verify token indices — they vary per pool deployment - [ ] Never use `get_virtual_price()` as a lending oracle without reentrancy guards - [ ] Deposit LP tokens into gauges for CRV emissions - [ ] Check pool A parameter — low A pools have higher slippage - [ ] Test against forked mainnet with real pool state