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Ethereum: BAD_DATA error when calling any contract function

As a developer working with Ethereum smart contracts, you have probably come across the infamous “BAD_DATA” error. This issue can occur when you try to call a contract function that expects data as input but receives an empty or invalid response.

In this article, we will delve into the cause of the BAD_DATA error and provide tips on how to resolve it in your Ethereum-based projects.

What is the BAD_DATA error?

The BAD_DATA error occurs when a contract recipient receives a response from a call that does not contain enough data. This can happen for several reasons:

• The request payload exceeds the expected size.

• The request payload contains invalid or malformed data.

• The response payload is empty or has insufficient data.

Causes of BAD_DATA

Before we move on to the solution, let’s look at some common causes of BAD_DATA error:

• Insufficient payload: If the contract receiver receives too little data as input, it may not be able to verify the function signature or perform the requested action.

• Incorrectly formatted data: Incorrectly formatted data can lead to errors during the call process.

• Empty response: An empty response from the contract receiver may indicate an error in processing the request.

Solutions to BAD_DATA

To resolve the BAD_DATA error, follow these steps:

1. Verify the contract function signature

Ensure that the contract function signature is correct and meets the expected input requirements.

contract MyContract {
function symbol() public view returns (string memory) {
// Return the requested data as a string
}
}

In this example, the symbol function expects a string input. Make sure you pass a valid string argument when calling the function.

2. Validate the request payload

Verify if the request payload contains any invalid or excessive data.

contract MyContract {
function symbol(data) public view returns (string memory) {
// Validate the request payload
require(msg.value.length >= 10, "Invalid input");
// Return a default message if validation fails
}
}

In this example, we validate the request payload by checking its length. If it is less than 10 bytes, an error is returned.

3. Handling an empty response

Implement a check to ensure that the response from the contract recipient contains sufficient data.

contract MyContract {
function symbol() public view returns (string memory) {
// Return a default message if no data is received
return "No data available";
}
}

In this example, we use the require statement to check if the response is empty. If there is none, a default message is returned.

4. Using a contract that supports BAD_DATA

Some Etherscan and Remix contracts are designed to handle BAD_DATA errors without having to implement specific checks or validation procedures.

contract MyContract {
function symbol() public view returns (string memory) {
// Return the requested data as a string
}
}

In this example, we simply return a default message if none is present. The contract receiver can handle this without any additional validation steps.

Best Practices

To avoid BAD_DATA errors in Ethereum-based projects:

• Always validate request payloads and response data before processing.

• Implement checks for empty or malformed data.

• Use contract functions designed to handle such cases.

• Perform thorough testing, especially when integrating with external services or APIs.