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

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

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);
    }
}