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Ethereum: Why My Contribution Method Fails with “Missing Restore Data”
As a developer working on a Solidity smart contract for an Initial Coin Offering (ICO), you’ve likely encountered a variety of issues that can hinder the success of your project. One common error that can occur during testing is the “missing restore data” issue, which affects the functionality of some contribution methods. In this article, we’ll dive into the causes of this error and provide tips on how to fix it in your contract.
What does “missing restore data” mean?
In Ethereum, a “restore” event occurs when an invalid or unsupported state is encountered during a transaction. This can happen for a variety of reasons, including:
- Invalid or Missing Contract Data
: If the internal variables of the contract are not initialized correctly, this can cause a restore.
- Invalid function calls: Functions that do not follow the standard Solidity syntax or use invalid parameter types can cause rollbacks.
- Uninitialized state variables: If the contract state is not properly set before using some functions, this can lead to rollbacks.
Why does my contribution method fail with “missing rollback data”?
Suppose your contribution method looks like this:
pragma solidity ^0.6.0;
contract TokenContributor {
address public owner;
public uint balance = 0;
// Function to contribute tokens
function contribute() public payable {
require ( msg . value >= 1 ether , " Invalid input " ) ;
if ( balance > 0 ) {
require(msg.value == balance *1 ether, "Tokens must equal the initial amount");
balance += msg.value;
} else {
// Add a revert condition here
} }
} }
} }
In this example, the contribute function checks if the user has contributed enough tokens and if their contribution is equal to the initial value. However, there is no revert statement to handle cases where an invalid or missing state variable is encountered.
Missing revert data error
If your contract encounters a revert event, it will stop executing and return control to the caller with an error message indicating that the input is invalid or the state has changed. This can cause your contribution method to fail if not handled correctly.
For example, let’s say you try to contribute 100 tokens but get a revert:
pragma solidity ^0.6.0;
contract TokenContributor {
address public owner;
public uint balance = 0;
// Function to contribute tokens
function contribute() public payable {
require ( msg . value >= 1 ether , " Invalid input " ) ;
if ( balance > 0 ) {
require(msg.value == balance *100 ether, "Number of tokens must equal initial amount");
balance += msg.value;
} else {
// Revert condition here
revert ( ) ;
} }
} }
} }
In this case, when a user tries to contribute 100 tokens but receives an invalid revert message, their contribution method will fail and stop execution.
Solving the “missing revert data” problem
To solve this problem, you need to add revert commands in your contract functions that can cause reverts. Here are some suggestions:
- Add a revert condition at the beginning of each function
: This will ensure that an error is raised if any invalid or missing state variables are encountered.
“`solidity
pragma solidity ^0.6.0;
contract TokenContributor {
address public owner;
public uint balance = 0;
// Function to pass tokens
function contribute() public payable {
require ( msg . value >= 1 ether , ” Invalid input ” ) ;
if ( balance > 0 ) {
require(msg.value == balance *100 ether, “Tokens must equal initial amount”);
balance += msg.