How to withdraw from the smart contract to the wallet

[enricocagliari]

Hi Everyone,

I managed to deploy the smart contract and perform the flash loans. However, I don't know how to withdraw the funds from the smart contract.
Let's talk with the case on hand:

• The flashloan transaction is https://kovan.etherscan.io/tx/0xeac15b9a14a8d37b100f23f9a55dca097369cb6ced33140e6efdf2b6f2d95c5f .
• My wallet is 0x5a4913ab8049779e5dd3195b0e81b9ea507bbae0
• The contract is 0xF5a1656C865Ed60ad4a3d5092A480a2BAff7af48

To do the flashloan, funds are transferred from wallet to the contract with transaction https://kovan.etherscan.io/tx/0x9c3d95bd9ddb14e7debfe9153724f7b3aaf0d981b4657d1a000e2d70860eff44 to cover the fees. Then I'm able to execute the flashloan correctly.

However, now the contract has a balance, that should be transferred back to my wallet. So my doubt is:

• How do I transfer the balance on the contract back to my wallet?
• Could be that the code is effectively transferring the profit back to the wallet, but I am not seeing it because there is no profit in the transaction I did? It was only the flashloan, so there is a loss for the fees.

Thanks for who can clarify me this.

[ch1ch0gz]

Hi,

FlashloanV2 is Withdrawable hence you can use the function withdraw.

Something like the below would withdraw all the weth you have in your flashloan for instance.

[enricocagliari]

Thank you @ch1ch0gz for your solution, at least this is a step forward.

Even though, when I run it, I get an error. Here is the response after running "brownie run scripts/withdraw_function.py --network kovan":

---

`Brownie v1.17.2 - Python development framework for Ethereum

AaveFlashloanMixFunzionaYesmodificareCopyProject is the active project.

Running 'scripts/withdraw_function.py::main'...
Getting flashloan contract...
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/_cli/run.py", line 51, in main
return_value, frame = run(
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/project/scripts.py", line 103, in run
return_value = f_locals[method_name](*args, **kwargs)
File "./scripts/withdraw_function.py", line 14, in main
tx = flashloan.Withdraw(weth, {"from": acct})
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/network/contract.py", line 763, in getattribute
raise AttributeError(f"Contract '{self._name}' object has no attribute '{name}'")
AttributeError: Contract 'FlashloanV2' object has no attribute 'Withdraw'`

---

Can you tell me what am I missing?

[ch1ch0gz]

Has your flashLoan contract got "contract FlashloanV2 is FlashLoanReceiverBaseV2, Withdrawable " withdrawable inherit?

[enricocagliari]

I think you are right, I do not have that line in any file, and I expecially paid attention at contract.py, and I do not have that line.
Can you provide the whole function, so I can add it there and see how it turns out to work?

[ch1ch0gz]

i think you are missing adding the import Withdrawable on FlashLoanReceiverBaseV2.sol

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

import { SafeMath } from '@openzeppelin/contracts/math/SafeMath.sol';
import { IERC20 } from '@openzeppelin/contracts/token/ERC20/IERC20.sol';
import { SafeERC20 } from '@openzeppelin/contracts/token/ERC20/SafeERC20.sol';
import { IFlashLoanReceiverV2 } from './../../../interfaces/v2/IFlashLoanReceiverV2.sol';
import { ILendingPoolAddressesProviderV2 } from './../../../interfaces/v2/ILendingPoolAddressesProviderV2.sol';
import { ILendingPoolV2 } from './../../../interfaces/v2/ILendingPoolV2.sol';
import "../../utils/Withdrawable.sol";

/** 
    !!!
    Never keep funds permanently on your FlashLoanReceiverBase contract as they could be 
    exposed to a 'griefing' attack, where the stored funds are used by an attacker.
    !!!
 */
abstract contract FlashLoanReceiverBaseV2 is IFlashLoanReceiverV2 {
  using SafeERC20 for IERC20;
  using SafeMath for uint256;

  ILendingPoolAddressesProviderV2 public immutable override ADDRESSES_PROVIDER;
  ILendingPoolV2 public immutable override LENDING_POOL;

  constructor(address provider) public {
    ADDRESSES_PROVIDER = ILendingPoolAddressesProviderV2(provider);
    LENDING_POOL = ILendingPoolV2(ILendingPoolAddressesProviderV2(provider).getLendingPool());
  }

  receive() payable external {}
}

And the Withdrawable.sol looks like

pragma solidity ^0.6.6;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

/**
    Ensures that any contract that inherits from this contract is able to
    withdraw funds that are accidentally received or stuck.
 */
 
contract Withdrawable is Ownable {
    using SafeERC20 for ERC20;
    address constant ETHER = address(0);

    event LogWithdraw(
        address indexed _from,
        address indexed _assetAddress,
        uint amount
    );

    /**
     * @dev Withdraw asset.
     * @param _assetAddress Asset to be withdrawn.
     */
    function withdraw(address _assetAddress) public onlyOwner {
        uint assetBalance;
        if (_assetAddress == ETHER) {
            address self = address(this); // workaround for a possible solidity bug
            assetBalance = self.balance;
            msg.sender.transfer(assetBalance);
        } else {
            assetBalance = ERC20(_assetAddress).balanceOf(address(this));
            ERC20(_assetAddress).safeTransfer(msg.sender, assetBalance);
        }
        emit LogWithdraw(msg.sender, _assetAddress, assetBalance);
    }
} 

[ch1ch0gz]

Has your flashLoan contract got "contract FlashloanV2 is FlashLoanReceiverBaseV2, Withdrawable " withdrawable inherit?

Here I was talking about Flashloan.sol which is another file you need to modify.

[enricocagliari]

@ch1ch0gz your advices here are outstanding. Me and probably all the people reading this thread owe you a big thank you.
Please check your email, I sent you something via GitHub :) .

Now, I was messing around with the code, I did not solve this mystery, but I have some error logs I want you to take a look at.

• First, I compared Withdrawable.sol and FlashLoanReceiverBaseV2.sol with the code you provided, and I can confirm I have the exact same code.
• Based on your response of March 16 2022, I created the file "withdraw_function.py" which has the following code:

---Code Begins---

from brownie import FlashloanV2, accounts, config, network, interface

def main():
"""
Withdraw Tokens from flashloanW
"""

acct = accounts.add(
    config["wallets"]["from_key"]
)
print("Getting flashloan contract...")
flashloan = FlashloanV2[len(FlashloanV2) - 1]
weth = interface.WethInterface(config["networks"][network.show_active()]["weth"])
tx = flashloan.Withdraw(weth, {"from": acct})
return flashloan

---Code Ends---

• I do not see a file Flashloan.sol, but I have FlashloanV2.sol, I guess this is the file you are referring to, right?

In my file I have the line "contract FlashloanV2 is FlashLoanReceiverBaseV2, Withdrawable" exactly as wrote by @PatrickAlphaC in https://github.com/brownie-mix/aave-flashloan-mix/blob/master/contracts/v2/FlashloanV2.sol

If I run "brownie run scripts/withdraw_function.py --network kovan" having the line "contract FlashloanV2 is FlashLoanReceiverBaseV2, Withdrawable" in FlashloanV2.sol I get:

---Code Begins---

Brownie v1.17.2 - Python development framework for Ethereum

Compiling contracts...
Solc version: 0.6.12
Optimizer: Enabled Runs: 200
EVM Version: Istanbul
Generating build data...

• OpenZeppelin/openzeppelin-contracts@3.0.0/Context
• OpenZeppelin/openzeppelin-contracts@3.0.0/Ownable
• OpenZeppelin/openzeppelin-contracts@3.0.0/SafeMath
• OpenZeppelin/openzeppelin-contracts@3.0.0/ERC20
• OpenZeppelin/openzeppelin-contracts@3.0.0/IERC20
• OpenZeppelin/openzeppelin-contracts@3.0.0/SafeERC20
• OpenZeppelin/openzeppelin-contracts@3.0.0/Address
• Withdrawable
• FlashloanV2
• FlashLoanReceiverBaseV2
• IFlashLoanReceiverV2
• ILendingPoolAddressesProviderV2
• ILendingPoolV2
• DataTypes

AaveFlashloanMixFunzionaYesmodificareCopyProject is the active project.

Running 'scripts/withdraw_function.py::main'...
Getting flashloan contract...
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/_cli/run.py", line 51, in main
return_value, frame = run(
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/project/scripts.py", line 103, in run
return_value = f_locals[method_name](*args, **kwargs)
File "./scripts/withdraw_function.py", line 12, in main
flashloan = FlashloanV2[len(FlashloanV2) - 1]
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/network/contract.py", line 174, in getitem
return self._contracts[i]
IndexError: list index out of range

---Code Ends---

Now, if I run "brownie run scripts/withdraw_function.py --network kovan" having the line you suggested "contract FlashloanV2_aave is FlashLoanReceiverBaseV2, Withdrawable" in FlashloanV2.sol I get:

---Code Begins---

Brownie v1.17.2 - Python development framework for Ethereum

Compiling contracts...
Solc version: 0.6.12
Optimizer: Enabled Runs: 200
EVM Version: Istanbul
Generating build data...

• OpenZeppelin/openzeppelin-contracts@3.0.0/Context
• OpenZeppelin/openzeppelin-contracts@3.0.0/Ownable
• OpenZeppelin/openzeppelin-contracts@3.0.0/SafeMath
• OpenZeppelin/openzeppelin-contracts@3.0.0/ERC20
• OpenZeppelin/openzeppelin-contracts@3.0.0/IERC20
• OpenZeppelin/openzeppelin-contracts@3.0.0/SafeERC20
• OpenZeppelin/openzeppelin-contracts@3.0.0/Address
• Withdrawable
• FlashloanV2_aave
• FlashLoanReceiverBaseV2
• IFlashLoanReceiverV2
• ILendingPoolAddressesProviderV2
• ILendingPoolV2
• DataTypes

AaveFlashloanMixFunzionaYesmodificareCopyProject is the active project.
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/_cli/run.py", line 51, in main
return_value, frame = run(
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/project/scripts.py", line 53, in run
module = _import_from_path(script)
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/project/scripts.py", line 149, in _import_from_path
_import_cache[import_str] = importlib.import_module(import_str)
File "/usr/lib/python3.9/importlib/init.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen, line line, in in
File "<frozen, line line, in in
File "<frozen, line line, in in
File "<frozen, line line, in in
File "<frozen, line line, in in
File "<frozen, line line, in in
File "./scripts/withdraw_function.py", line 1, in
from brownie import FlashloanV2, accounts, config, network, interface
ImportError: cannot import name 'FlashloanV2' from 'brownie' (/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/init.py)

---Code Ends---

Said all that, still the withdrawal from the smart contract to the wallet does not get execute successfully. Suggestions?

[ch1ch0gz]

Can you quickly try having

in your FlashloanV2.sol contract instead of

Flashloan_aave is a different flashloan I am playing with.

[enricocagliari]

The response is get is :

Brownie v1.17.2 - Python development framework for Ethereum

Compiling contracts...
Solc version: 0.6.12
Optimizer: Enabled Runs: 200
EVM Version: Istanbul
Generating build data...

OpenZeppelin/openzeppelin-contracts@3.0.0/Context
OpenZeppelin/openzeppelin-contracts@3.0.0/Ownable
OpenZeppelin/openzeppelin-contracts@3.0.0/SafeMath
OpenZeppelin/openzeppelin-contracts@3.0.0/ERC20
OpenZeppelin/openzeppelin-contracts@3.0.0/IERC20
OpenZeppelin/openzeppelin-contracts@3.0.0/SafeERC20
OpenZeppelin/openzeppelin-contracts@3.0.0/Address
Withdrawable
FlashloanV2
FlashLoanReceiverBaseV2
IFlashLoanReceiverV2
ILendingPoolAddressesProviderV2
ILendingPoolV2
DataTypes

Running 'scripts/withdraw_function.py::main'...
Getting flashloan contract...
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/_cli/run.py", line 51, in main
return_value, frame = run(
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/project/scripts.py", line 103, in run
return_value = f_locals[method_name](*args, **kwargs)
File "./scripts/withdraw_function.py", line 12, in main
flashloan = FlashloanV2[len(FlashloanV2) - 1]
File "/usr/local/lib/python3.9/dist-packages/eth_brownie-1.17.2-py3.9.egg/brownie/network/contract.py", line 174, in getitem
return self._contracts[i]
IndexError: list index out of range

[Abdel364]

@ch1ch0gz thank you i solved it with your guide i want to send you an email to say thank you but i didn't find your email

[Allegoryof]

@ch1ch0gz Hello i just sent you a message on twitter, i just saw this and i'd need your assistance