The operate function starts from performing few sanity checks. We are looking at this code:

Liquidity layer

Remember that this function handles all operations in one place:

  • supplyAmount > 0 -> we are doing a regular supply
  • supplyAmount < 0 -> we are withdrawing liquidity
  • borrowAmount > 0 -> we are doing a regular borrow
  • borrowAmount < 0 -> we are paying back borrowed assets

So we perform straightforward sanity checks in this order:

  1. Making sure we are not supplying or borrowing zero amount of tokens

  2. Making sure supply and borrow amounts are in the correct range of type(int128).

    Although amounts are int256 when calling the operate function, we are checking for the type(int128) range because it gives us flexibility later, knowing that we can fit two variables in 256 bits. For example, when calculating total liquidity passed as deposit + payback.

  3. Making sure we are not withdrawing or borrowing to the zero address

  4. Making sure we passed msg.value for the native token

    Like the majority of protocols, Fluid uses a standard convention to represent the native token address as:

    /// @dev address that is mapped to the chain native token
address internal constant NATIVE_TOKEN_ADDRESS = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;