Get a state variable from unverified contract

Question

Is it possible to get a variable state from existing contract which was not verified but I know what variables, functions etc. the contract contains?

Assume, we have the following script (using Brownie, the name of variable is variable_to_obtain):

from brownie import Contract
from scripts.helpers import get_account


def get_variable_of_instance(instance_address):
    account = get_account()
    instance_contract = Contract.from_explorer(instance_address, {"from": account})
    variable_to_return = instance_contract.variable_to_obtain()
    return variable_to_return


def main():
    var = get_variable_of_instance("address_of_instance")
    print(var)

Any idea? Thank you so much.

Answer 1

The way how to do this depends on the contract that you want to extract the variable from.

If the contract normally provides a function to query this variable you just need to know the correct function id to query it.

If this is not the case then you can use eth_getStorageAt to query the storage at a specific slot for that contract, but for this you will require some knowledge about the internals of that contract.