aave-protocol-v2/contracts/misc/WalletBalanceProvider.sol

// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.6.8;

import "@openzeppelin/contracts/utils/Address.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

import "../configuration/LendingPoolAddressesProvider.sol";
import "../lendingpool/LendingPoolCore.sol";
import "../libraries/EthAddressLib.sol";


/**
* @title WalletBalanceProvider contract
* @author Aave, influenced by https://github.com/wbobeirne/eth-balance-checker/blob/master/contracts/BalanceChecker.sol
* @notice Implements a logic of getting multiple tokens balance for one user address
* @dev NOTE: THIS CONTRACT IS NOT USED WITHIN THE AAVE PROTOCOL. It's an accessory contract used to reduce the number of calls
* towards the blockchain from the Aave backend.
**/
contract WalletBalanceProvider {

    using Address for address;

    LendingPoolAddressesProvider provider;

    constructor(LendingPoolAddressesProvider _provider) public {

        provider = _provider;

    }
    /**
    @dev Fallback function, don't accept any ETH
    **/
    receive() external payable {
        revert("WalletBalanceProvider does not accept payments");
    }

    /**
    @dev Check the token balance of a wallet in a token contract

    Returns the balance of the token for user. Avoids possible errors:
      - return 0 on non-contract address
    **/
    function balanceOf(address _user, address _token) public view returns (uint256) {
        // check if token is actually a contract
        if (_token.isContract()) {
            return IERC20(_token).balanceOf(_user);
        } else {
            return 0;
        }
    }

    /// @notice Fetches, for a list of _users and _tokens (ETH included with mock address), the balances
    /// @param _users The list of users
    /// @param _tokens The list of tokens
    /// @return And array with the concatenation of, for each user, his/her balances
    function batchBalanceOf(address[] memory _users, address[] memory _tokens) public view returns (uint256[] memory) {
        uint256[] memory balances = new uint256[](_users.length * _tokens.length);

        for (uint256 i = 0; i < _users.length; i++) {
            for (uint256 j = 0; j < _tokens.length; j++) {
                uint256 _offset = i * _tokens.length;
                if (_tokens[j] == EthAddressLib.ethAddress()) {
                    balances[_offset + j] = _users[i].balance; // ETH balance
                } else {
                    if (!_tokens[j].isContract()) {
                        revert("INVALID_TOKEN");
                    } else {
                        balances[_offset + j] = balanceOf(_users[i], _tokens[j]);
                    }
                }
            }
        }

        return balances;
    }


    /**
    @dev provides balances of user wallet for all reserves available on the pool
    */
    function getUserWalletBalances(address _user) public view returns (address[] memory, uint256[] memory) {

        LendingPoolCore core = LendingPoolCore(provider.getLendingPoolCore());

        address[] memory reserves = core.getReserves();

        uint256[] memory balances = new uint256[](reserves.length);

        for (uint256 j = 0; j < reserves.length; j++) {
            if(!core.getReserveIsActive(reserves[j])){
                balances[j] = 0;
                continue;
            }
            if (reserves[j] != EthAddressLib.ethAddress()) {
                balances[j] = balanceOf(_user, reserves[j]);
            } else {
                balances[j] = _user.balance; // ETH balance
            }
        }

        return (reserves, balances);
    }
}