Reading Asset Balances

As noted in Best Practices, the AssetSink's available asset balance is observed in three places:

• the contract address of the AssetSink itself
• the UniswapV3Pool contract addresses
• the UniswapV2Pair liquidity tokens

For example, the releasable USDC balance is USDC.balanceOf(address(assetSink)) + sum of UniswapV3Pool.protocolFees() + sum of UniswapV2Pair.burn() for each USDC-paired pool

Uniswap v3 Pool Protocol Fees

Reading available Uniswap v3 Pool protocol fees requires calling .protocolFees() on each UniswapV3Pool contract

import {IERC20} from "forge-std/interfaces/IERC20.sol";
import {IUniswapV3Pool} from "@uniswap/v3-core/contracts/interfaces/pool/IUniswapV3Pool.sol";
import {IAssetSink} from "@uniswap/phoenix-fees/src/interfaces/IAssetSink.sol";

contract Example {
    IAssetSink assetSink = IAssetSink(0x0);

    function releaseableBalance(address token, address[] calldata pools)
        external
        view
        returns (uint256)
    {
        return IERC20(token).balanceOf(address(assetSink)) 
            + _getV3ProtocolFeesUnclaimed(token, pools); 
    }

    function _getV3ProtocolFeesUnclaimed(address token, address[] calldata pools)
        internal
        view
        returns (uint256 feesUnclaimed)
    {
        uint128 token0Unclaimed;
        uint128 token1Unclaimed;
        for (uint256 i; i < pools.length; i++) {
            (token0Unclaimed, token1Unclaimed) = IUniswapV3Pool(pools[i]).protocolFees(); 

            // determine if the requested `token` parameter is `pool.token0()` or `pool.token1()`
            feesUnclaimed += pool.token0() == token
                ? token0Unclaimed
                : pool.token1() == token
                ? token1Unclaimed
                : 0;
        }
    }
}

Because unclaimed tokens are stored in Uniswap v3 Pool contracts, integrators should use offchain indexing to track which pools contain the asset of interest. For example, USDC protocol fees are accrued in many different pools:

• USDC / TOKENA 0.05% Fee
• USDC / TOKENA 0.30% Fee
• USDC / TOKENB 0.30% Fee
• USDC / TOKENC 0.30% Fee
• and so on...

To track which pools contain the asset of interest, we recommend to index the PoolCreated event emitted by the UniswapV3Factory contract

Uniswap v2 Pool Protocol Fees

Uniswap v2 protocol fees are automatically "pushed" to the AssetSink so no additional calls are required to make the assets releasable. However, Uniswap v2 protocol fees are accrued in the form of liquidity tokens (LP tokens) which are redeemable for underlying assets. Ownership of the LP token represents the proportional share of the pool's assets.

(LP Token Balance / LP Token Total Supply) * Pool Reserves

IERC20 lpToken;

uint256 amount0 = (lpToken.balanceOf(address(assetSink)) * IERC20(lpToken.token0()).balanceOf(address(lpToken))) / lpToken.totalSupply();
uint256 amount1 = (lpToken.balanceOf(address(assetSink)) * IERC20(lpToken.token1()).balanceOf(address(lpToken))) / lpToken.totalSupply();

(uint256 amount0, uint256 amount1) = IUniswapV2Pair(pool).burn(recipient);