Ethereum: Gas estimation error when interacting with smart contracts

As a developer working with smart contracts on the Ethereum network, it is essential to ensure that your code is efficient and uses gas optimally. One common problem that can arise when interacting with smart contracts is a gas estimation error, which can lead to unexpected behavior or even rollbacks.

In this article, we will examine how a simple smart contract example can introduce a gas estimation error and provide guidance on how to identify and fix the problem.

Problem: Gas estimation error

Let’s look at the “pay” function in the smart contract example:

pragma power ^0.4.21;
contract PayMultiple {
function pay(address[] payees, unit values) public pay{
for (uint i = 0; i < beneficiaries.length; i++) {
emit Transfer(payees[i], sender, values[i]);
}
}
}

In this code, the `pay'' function iterates through an array of addresses and sends a certain number of tokens to each address using theTransfer'' event. However, when dealing with multiple recipients, an error in gas estimation can lead to unexpected behavior.

Problem: Multiple Gas Estimation

When you call thepay'' function from Remix or any other Ethereum client, it estimates the amount of gas needed to fulfill the contract. In our case, thepay'' function iterates through an array of addresses and sends a certain number of tokens to each address. If we are dealing with multiple recipients, the estimated amount of gas can be much larger than expected.

For example, let's say we have 1000 recipients, each receiving 10 tokens. The estimated gas in this scenario would be:

• 1000 addresses x 10 tokens per address = 10000 gas

• Assuming an average gas price of 2000 gas per unit (a reasonable estimate), total gas requirement: 10000 / 2000 ≈ 50 units

However, if we call thepay’ function from Remix or another client, it may only send 1 token to each address and use a significant amount of gas. This can lead to unexpected behavior, such as:

• Canceling due to excessive gas consumption

• Unbalanced transfer amounts

• Incorrect recipient addresses

Fix: Using `Transfer'' with gas

To avoid these problems, we can modify thepay'' function to use thetransfer'' event instead of thetransfer'' message. This allows us to pass the amount of gas as an argument.

pragma power ^0.4.21;
contract PayMultiple {
function payment(address[] payees, unitvalues) public payment{
for (uint i = 0; i < beneficiaries.length; i++) {
transfer(payees[i], values[i]);
}
}
function transfer(address payee, uint amount) public override payable {
request(transferable(msg.sender), "You must callpay` with a fuel estimation function.");
request(amount > 0, "Amount cannot be zero or negative.");
// Calculate the estimated gas quantity for this transaction
request(msg.value * quantity / 2000000000000 < totalGas(), "The estimated gas exceeds the maximum allowed value.");
// Call the transfer function from Remix or another client
emit Transfer(recipient, sender, amount);
}
}

Benefits of using “transfer”

Using the “transfer” event with the gas estimation function provides several benefits:

• Reduced gas consumption: Since we pass the gas amount as an argument, we don’t have to estimate it using the gas estimation algorithm.

• Simplified code: The “transfer” function automatically handles sending and receiving gas.

• Improved error handling: We can catch gas consumption-related errors and provide more informative feedback.

Conclusion

In short, a simple smart contract example like the one above can cause a gas estimation error when interacting with contracts.