Data dependency

Data dependency

Data dependency allows knowing if the value of a given variable is influenced by another variable's value.

Because smart contracts have a state machine based architecture, the results of the data dependency depend on the context (function/contract) of the analysis. Consider the following example:

contract MyContract{
    uint a = 0;
    uint b = 0;

    function setA(uint input_a) public{
        a = input_a;
    }

    function setB() public{
        b = a;
    }

}

In this example, if we consider only setA, we have the following dependency:

• a is dependent on input_a

If we consider only setB, we have:

• b is dependent on a

If we consider the contract entirely (with all the functions), we have:

• a is dependent on input_a
• b is dependent on a and input_a (by transitivity)

slither.analyses.is_dependent(variable, variable_source, context) allows to know if variable is dependent on variable_source on the given context.

As a result, in our previous example, is_dependent(b, a, funcA) will return False, while is_dependent(b, a, myContract) will return True:

from slither import Slither
from slither.analyses import is_dependent

slither = Slither('data_dependency_simple_example.sol')

myContract = slither.get_contract_from_name('MyContract')
funcA = myContract.get_function_from_signature('setA(uint256)')
input_a = funcA.parameters[0]

a = myContract.get_state_variable_from_name('a')
b = myContract.get_state_variable_from_name('b')

print(f'{b.name} is dependant from {input_a.name}?: {is_dependent(b, a, funcA)}')
print(f'{b.name} is dependant from {input_a.name}?: {is_dependent(b, a, myContract)}')