To call flash, the flash parameters for the initial call are required, as well as any other parameters you’d like to pass through to the callback.
The FlashParams struct will contain the addresses of the tokens and the amounts we want to extract from the pool.
struct FlashParams {
address token0;
address token1;
uint256 amount0;
uint256 amount1;
}
The FlashCallbackData struct must contain the data we want to send to the callback. This includes poolKey, which expresses the sorted tokens returned by the PoolAddress library.
struct FlashCallbackData {
uint256 amount0;
uint256 amount1;
address payer;
PoolAddress.PoolKey poolKey;
}
From this point, we are starting our function by assigning the appropriate parameters from the Flashparams (which we have declared in memory as params) to our variable poolKey
function initFlash(FlashParams memory params) external {
PoolAddress.PoolKey memory poolKey =
PoolAddress.PoolKey({token0: params.token0, token1: params.token1);
}
The next step is to declare pool as type [IAlgebraPool], which allows us to call flash on the desired pool contract.
IAlgebraPool pool = IAlgebraPool(PoolAddress.computeAddress(factory, poolKey));
Finally, we call flash on the previously declared pool. In the last parameter, we abi.encode the FlashCallbackData, which will be decoded in the callback and aimed at informing about the next steps of the particular transaction.
pool.flash(
address(this),
params.amount0,
params.amount1,
abi.encode(
FlashCallbackData({
amount0: params.amount0,
amount1: params.amount1,
payer: msg.sender,
poolKey: poolKey
})
)
);
}
The full function:
struct FlashParams {
address token0;
address token1;
uint256 amount0;
uint256 amount1;
}
struct FlashCallbackData {
uint256 amount0;
uint256 amount1;
address payer;
PoolAddress.PoolKey poolKey;
}
function initFlash(FlashParams memory params) external {
PoolAddress.PoolKey memory poolKey =
PoolAddress.PoolKey({token0: params.token0, token1: params.token1});
IAlgebraPool pool = IAlgebraPool(PoolAddress.computeAddress(factory, poolKey));
pool.flash(
address(this),
params.amount0,
params.amount1,
abi.encode(
FlashCallbackData({
amount0: params.amount0,
amount1: params.amount1,
payer: msg.sender,
poolKey: poolKey
})
)
);
}