Missing rollback data: a potential bug in Ethereum Hardhat and Ganache
Ethereum, like any other blockchain platform, is not immune to bugs. In the context of Hardhat, a popular development environment for Ethereum smart contracts, missing rollback data can occur. This error occurs when the contract attempts to rollback an invalid opcode but fails to retrieve the necessary rollback data.
The Problem: Missing Rollback Data
When a transaction goes wrong in an Ethereum smart contract, the contract execution engine throws an exception. In this case, the exception is usually a “RuntimeError” due to a VM (virtual machine) error. The error message usually indicates that the VM encountered an invalid opcode. However, sometimes, the underlying problem can be more complex and require additional data.
Hardhat and Ganache: The Environment
Hardhat is a development environment designed for the development of Ethereum smart contracts using Solidity. It is based on Web3.js and provides tools like Ganache for local testing of contracts without deploying them to the mainnet. When you use Hardhat or Ganache, you rely on their internal state management systems to maintain the virtual machine.
The Problem: Missing Revert Data in Hardhat/Ganache
In Hardhat and Ganache, missing revert data is particularly problematic because it can cause unexpected behavior or errors when trying to recover from the execution of a contract. The revertData field of the error object may be empty or null, indicating that the contract was unable to retrieve the necessary revert data.
Example Error
Here is an example of what the error message might look like:
{
"error": {
"message": "VM Exception processing transaction: Invalid opcode",
"stack": [
"RuntimeError: VM Exception processing opcode at index 0 of [0x...]"
]
},
"info": {
"dataRevert": null // or empty string
}
}
In this case, the contract attempted to revert an invalid opcode but was unable to retrieve the necessary revert data (“dataRevert”).
Troubleshooting
To resolve missing data revert errors in Hardhat and Ganache:
- Check your error messages – Review the stack trace to identify which opcode is causing the problem.
- Check contract state – Ensure that the internal state of the contract is correct before attempting to rollback an invalid opcode.
- Use the
revertDatafield
– Check if the
revertDatafield exists and is not empty. If so, update your code to retrieve the necessary rollback data.
Best practices
To minimize errors when working with missing rollback data:
- Test in local environments – Use Hardhat or Ganache locally before deploying contracts to the mainnet.
- Use the
revertDatafield – Always check if thedataRevertfield is complete and update your code accordingly.
By being aware of the potential issue of missing rollback data, developers can take steps to prevent and fix this bug, ensuring more reliable and maintainable smart contract development on Ethereum environments like Hardhat and Ganache.