Blockchain Flashloan Lets get Front-runned!
I've written an article that walks through more about this code and project : https://medium.com/@harshgill2954/my-flash-loan-arbitrage-stolen-by-front-runners-for-education-19dbe0f88063. Essentially, this code is for GETTING FRONT-RUNNED. It's a fun example that I wanted to showcase so everyone can better understand and learn what front-running is like! This Repo if you use it on the BSC mainnet, WILL MOST LIKELY GET FRONT-RUNNED!
The aim is to walk through how front-running can occur on the Blockchain network. The code is not meant for production and is unoptimized.
It uses 2 main smart contracts :
-
A flashswap contract
contracts/FlashSwap.sol::brownie-frontrun-arb: This contract is able to borrow flashloans and execute functions to perform some operations and then return back the borrowed loans with interest. It uses the Pancakeswap's IUniswapV2Pair and calls it with a non-zero data parameter, which then triggers a flashloan in a callback function defined as pancakecall. -
A opportunity contract
contracts/Opportunity.sol::brownie-frontrun-arb: This contract simply pays out its entire balance to any user who knows the input of some KECCAK256 hash and who transfers 0.1 Unit of some set ERC20 token. It is initially funded with 5 BUSD of the unlocked accounts money, or by an impersonated whale if you run it on the forked network.
Deployment
To deploy the logic of this entire system, you can deploy the transactions on the testnet or mainnet for Binance Smart Chain. For mainnet, do change the private_key and is_true variable inside the deploy_contracts.py script. To run it locally would require a deployment of BUSD ERC20 token along with a liquidity pool, so to save headache just rely on using the bsc networks.
Before running the scripts you need to download the following dependencies:
pip3 install brownie
brownie pm install Uniswap/v2-core@1.0.0
brownie pm install OpenZeppelin/openzeppelin-contracts@4.8.2To run the scripts simply type :
brownie run scripts/deploy_contracts --network bsc-main-forkThis returns
Brownie v1.17.2 - Python development framework for Ethereum
TokenProject is the active project.
Launching 'ganache-cli --accounts 10 --hardfork istanbul --fork https://bsc-dataseed.binance.org --gasLimit 12000000 --mnemonic brownie --port 8545 --chainId 56'...
Running 'scripts/deploy_contracts.py::main'...
Transaction sent: 0x91238cbad645f1b61e7bf49dc9e035b71548e5515fa0caa277ab8c3e4148dfd6
Gas price: 0.0 gwei Gas limit: 12000000 Nonce: 3846
FlashSwapPancake.constructor confirmed Block: 26859911 Gas used: 688365 (5.74%)
FlashSwapPancake deployed at: 0x4A801468300b497AB11e368C90a505e93D574aF0
Transaction sent: 0x998a2cd6700228b86e096716cae2ecc6891472d8e58f8fb18ccfd68007d9c17c
Gas price: 0.0 gwei Gas limit: 12000000 Nonce: 3847
Opportunity.constructor confirmed Block: 26859912 Gas used: 585241 (4.88%)
Opportunity deployed at: 0x012c5C564c3E061ec5bB36E99D56EE364bAb7C49
Transaction sent: 0x0716c5490142205ff104511ff4d9e75069a7684ef5dbd2e69986ce248f426e19
Gas price: 0.0 gwei Gas limit: 12000000 Nonce: 3848
FlashSwapPancake.withdrawAllBalance confirmed Block: 26859913 Gas used: 31948 (0.27%)
FlashSwapPancake.withdrawAllBalance confirmed Block: 26859913 Gas used: 31948 (0.27%)
Transaction sent: 0x8e0cc635d7349ee7e98fc8cbd3b5bc21ce2dd5f1e6f945ed93506f7c804626fb
Gas price: 0.0 gwei Gas limit: 12000000 Nonce: 3849
Opportunity.withdrawAllBalance confirmed Block: 26859914 Gas used: 31957 (0.27%)
Opportunity.withdrawAllBalance confirmed Block: 26859914 Gas used: 31957 (0.27%)
Transaction sent: 0xf10eae1b8b1d7c670b5c8beb264abd4b78b0c7aefaf57c42e9893ae85fbdb119
Gas price: 0.0 gwei Gas limit: 12000000 Nonce: 3850
IERC20.transfer confirmed Block: 26859915 Gas used: 36103 (0.30%)
IERC20.transfer confirmed Block: 26859915 Gas used: 36103 (0.30%)
Transaction sent: 0x34e40a68ce32c5b9266de4d4617e04d8e7dd223c3bfa776e66444d3bc5e67e4d
Gas price: 0.0 gwei Gas limit: 12000000 Nonce: 3851
IERC20.transfer confirmed Block: 26859916 Gas used: 36103 (0.30%)
IERC20.transfer confirmed Block: 26859916 Gas used: 36103 (0.30%)
Initial Fund FlashSwap balance: 1000000000000000000
Transaction sent: 0x2e7859cb3de747d9b3154596ed65f8c51d302443420a320928a684d34172bea1
Gas price: 0.0 gwei Gas limit: 12000000 Nonce: 3852
FlashSwapPancake.borrowFlashloan confirmed Block: 26859917 Gas used: 150239 (1.25%)
FlashSwapPancake.borrowFlashloan confirmed Block: 26859917 Gas used: 150239 (1.25%)
Final FlashSwap balance: 5996990972918756268
Final Opportunity balance: 0
Final profit: 4996990972918756268Testing
To run the tests and check the gas of each tranasction for interesting and a prettified response:
brownie test --network bsc-main-fork --gasLaunching 'ganache-cli --accounts 10 --hardfork istanbul --fork https://bsc-dataseed.binance.org --gasLimit 12000000 --mnemonic brownie --port 8545 --chainId 56'...
tests/test_flashswap_flow.py .... [100%]
================================================================ Gas Profile =================================================================
FlashSwapPancake <Contract>
├─ constructor - avg: 688365 avg (confirmed): 688365 low: 688365 high: 688365
├─ borrowFlashloan - avg: 150239 avg (confirmed): 150239 low: 150239 high: 150239
└─ withdrawAllBalance - avg: 24816 avg (confirmed): 25348 low: 22693 high: 25348
Opportunity <Contract>
├─ constructor - avg: 585241 avg (confirmed): 585241 low: 585241 high: 585241
├─ solveHashAndPay - avg: 43800 avg (confirmed): 43800 low: 43800 high: 43800
└─ withdrawAllBalance - avg: 24831 avg (confirmed): 25357 low: 22731 high: 25357
Token <Contract>
├─ transfer - avg: 51103 avg (confirmed): 51103 low: 51091 high: 51115
└─ approve - avg: 44094 avg (confirmed): 44094 low: 44094 high: 44094
============================================================= 4 passed in 14.10s =============================================================The unit tests included are quite basic and the relevant fixtures for the test are defined in tests/conftest.py::brownie-frontrun-arb fixture.