✍️Gas Saving Technique 16: Early Validation before external call

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Introduction

In smart contract development on Ethereum, conserving gas is a top priority. A notable practice to achieve gas efficiency is performing validation checks as early as possible in the function, ideally before making external calls. Early validation not only enhances the contract's security but also prevents unnecessary gas expenditure by terminating the execution early in case of invalid conditions.

Impact & Details

Understanding Gas Consumption

• Gas Cost of External Calls: External calls are expensive in terms of gas usage. If a function makes an external call and later finds out a condition isn’t met (through validation), the gas spent on the external call is wasted.

• Early Validation Benefits: By conducting necessary validation checks before external calls, you can ensure that the function only proceeds with these calls when conditions are met, saving gas in scenarios where the call would be unnecessary.

How to Implement Early Validation for Gas Savings

Practical Example: Early Validation Optimization

Here’s a contract function example before and after implementing early validation:

Before Optimization:

solidityCopy code// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IExternalContract {
    function externalFunction() external;
}

contract MyContract {
    IExternalContract public externalContractInstance;
    uint256 public threshold;

    function myFunction(uint256 amount) public {
        externalContractInstance.externalFunction();  // External call before validation
        require(amount >= threshold, "Amount below threshold");  // Validation after external call
        // ... rest of the function ...
    }
}

After Optimization:

solidityCopy code// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IExternalContract {
    function externalFunction() external;
}

contract MyContract {
    IExternalContract public externalContractInstance;
    uint256 public threshold;

    function myFunction(uint256 amount) public {
        require(amount >= threshold, "Amount below threshold");  // Early validation
        externalContractInstance.externalFunction();  // External call after validation
        // ... rest of the function ...
    }
}

In the optimized version, the validation check is moved before the external call, saving gas when the require condition isn't met.

Recommended Mitigation Steps

1. Identify Late Validations: Review your smart contracts to locate validation checks that occur after external calls.

2. Rearrange Validations: Move validation checks to occur as early as possible in the function, preferably before any external calls.

3. Test: Rigorously test the contract after rearrangement to ensure it maintains its functionality while efficiently saving gas.

Conclusion

Implementing validation checks early in the function, especially before making external calls, is a simple and effective optimization technique for gas saving in smart contract development. The practice is crucial in scenarios where external calls are costly, ensuring that gas isn't wastefully expended when conditions aren’t met. Always ensure to test the contract extensively after such optimizations to validate its functionality and gas efficiency.