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How to integrate Curve smart contracts

First of all, you'll need to know the contract's ABI. Addresses of the contract and the token representing liquidity are here.

Next is the breif description of methods you need to fascilitate exchanges.

Getting static information

coins: public(address[N_COINS])
  • By calling contract.coins(i), you get contract address of i-th c-token (cDAI, cUSDC, ...); i = 0, 1, ....
underlying_coins: public(address[N_COINS])
  • By calling contract.underlying_coins(i), you get contract address of i-th token (DAI, USDC, ...).

Both those methods don't change the state.

Getting price for c-tokens (cDAI, cUSDC)

def get_dy(i: int128, j: int128, dx: uint256) -> uint256:

How much of c-token j you'll get in exchange for dx of c-token i, including the fee. For example, get_dy(0, 1, dx) will give you amount of cUSDC you'll get for dx of cDAI.

This method doesn't change the state.

Getting price for underlying tokens (DAI, USDC)

def get_dy_underlying(i: int128, j: int128, dx: uint256) -> uint256:

How much of underlying token j you'll get in exchange for dx of token i, including the fee. For example, get_dy_underlying(0, 1, dx) will give you amount of USDC you'll get for dx of DAI.

This method doesn't change the state.

Exchanging c-tokens

def exchange(i: int128, j: int128, dx: uint256, min_dy: uint256):

This method exchanges dx of c-token i into c-token j. You specify min_dy as the minimal amount of c-token j to get to avoid front-running. You can also use deadline to make transaction revert if it wasn't accepted for too long.

Used to exchange cDAI<>cUSDC (and analogues in future deployments).

Exchanging underlying tokens

def exchange_underlying(i: int128, j: int128, dx: uint256, min_dy: uint256):

This method exchanges dx of underlying token i into token j. You specify min_dy as the minimal amount of token j to get to avoid front-running. You can also use deadline to make transaction revert if it wasn't accepted for too long.

Used to exchange DAI<>USDC (and analogues in future deployments).

Bonus: measuring profits

def get_virtual_price() -> uint256:

This read-only methods calculates price of liquidity share. In order to calculate profits between two points, you measure virtual price in those two moments and divide later by the earlier, and subtract 1.

The method doesn't measure the real price in dollars, but rather profit on top of what you would have observe with fee-less exchange. It is not affected by market fluctuations, and can measure returns even in a volatile market, over any periods of time.