Extracting Readable/Writable State Variables from an Ethereum Smart Contract

As Ethereum-based decentralized applications (dApps) become more popular, it is becoming increasingly important to understand how they store data on the blockchain. In this article, we will look at methods for extracting readable and writable state variables from a smart contract written in Solidity.

Understanding Ethereum State

In an Ethereum smart contract, state is represented as an object that stores data. Each object can have multiple properties (state variables) that are accessed using dot or bracket notation. For example:

pragma solidity ^0.8.0;
contract MyContract {
uint public counter; // readonly variable
mapping(address => uint) public note; // map of user addresses to counters
function incrementCounter() public payable {
counter += 1 ;
}
function updateMemo(address _user, uint amount) public {
memo[_user] = amount;
}
}

In this example, the counter variable is a read-only property, accessed using dot notation (MyContract.counter). The memo tab is also a read-only property, accessed using bracket notation (MyContract.memo["user"]).

Extracting read-write sets of state variables

To extract read-write sets of state variables from an Ethereum smart contract, the following approaches can be used:

• Get all properties: Use solhint get-variables or solc get-variable-counts to get a list of all the properties (state variables) of the contract.

• Using reflection: You can use Solidity’s reflection function (solc --reflection) to inspect and modify the state variables of the contract at runtime.

Example: Extracting Read-Write State Variable Sets

Assuming we have an Ethereum smart contract called “MyContract” with a read-only variable “counter” and a writable set “memo”, we can perform the following steps:

• Get all properties using the command “solhint get-variables MyContract”:

$ solhint get-variables MyContract
Counter: uint
Note: mapping(address => uint)

• Inspect and modify the contract state variables at runtime using Solidity’s reflection function (solc –reflection) with the following command:

$ solc --reflection --print-vars MyContract

Read-only variable
Counter (uint)

Writable set
Note: mapping(address => uint)

Note that the --print-vars flag is used to print all variables in the contract, including readable and writable variables and internal variables.

Conclusion

Extracting a set of readable and writable state variables from an Ethereum smart contract requires a combination of Solidity’s reflection functions, solhint, and perhaps manual inspection with Solscan or other tools. By understanding how to use these techniques, you will be better able to analyze and understand the behavior of your own Ethereum smart contracts.

Recommendations

• Use solhint get-variables to retrieve a list of all properties (state variables) of a contract.

• Use Solidity’s reflection function (solc --reflection) with the --print-vars flag to inspect and modify the state variables of the contract at runtime.

• Consider using Solscan or other tools to help you identify and extract information about your smart contracts.