Memory leak for the `fromWei` utility function for stirng input

[nazarhussain]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

If the input value for the fromWei function is a string type, it leaks the memory and heap continuously increased.

Expected Behavior

There should not be a memory leak regardless of the type of input.

Steps to Reproduce

// test.js
const { fromWei } = require('web3-utils');

const limit = 2_000_000;

const toKb = num => (num / 1024).toFixed();

new Array(limit).fill('10000').forEach((d, i) => {
	if (i % 10000 === 0) {
		const mem = process.memoryUsage();
		console.log(`heap: ${toKb(mem.heapUsed)}, total: ${toKb(mem.heapTotal)} rss: ${toKb(mem.rss)}`);
	}
	fromWei(d, 'ether');
});

Start the node process with following options.

NODE_OPTIONS=--max-old-space-size=500 node test.js

Web3.js Version

4.x

Environment

• Operating System: Mac/Linux
• Node.js Version: 16.6
• NPM Version: 8.11

Anything Else?

This behaviour was not seen with the 1.x.

[mpetrunic]

The leak is in web3-validator specifically ajv so the issue should be renamed. Ajv is using object ref as a key for caching compiled schema so every validate(['uint'], 123) is compiled and cached separately. #5574 tries to reduce the leak but it's not perfect.

A better solution would be to precompile all the used schemas or implement custom validation for validating primitive types.