[KMP] Fix issue: memory leak found in Base58.decode in iOS

[10gic]

Description

Fix issue #4030

How to test

Run Rust, C++, Kotlin, Swift tests

Types of changes

Checklist

• Create pull request as draft initially, unless its complete.
• Add tests to cover changes as needed.
• Update documentation as needed.
• If there is a related Issue, mention it in the description.

If you're adding a new blockchain

• I have read the guidelines for adding a new blockchain.

Screenshots

Before fixing, run Base58.decode 100000 times, it takes up to 200 MB of memory:

After fixing, run Base58.decode 100000 times, it takes up to 97.4 MB of memory:

Solution

The generated code before fixing:

package com.trustwallet.core

actual object Base58 {

    // ......

    actual fun decode(string: String): ByteArray? =
        TWBase58Decode(string.toTwString()).readTwBytes()         // toTwString and readTwBytes leak memory!


    // ......
}

Definition of old readTwBytes:

internal fun COpaquePointer?.readTwBytes(): ByteArray? =
    TWDataBytes(this)?.readBytes(TWDataSize(this).toInt())

The generated code after fixing:

package com.trustwallet.core

actual object Base58 {

    // ......

    actual fun decode(string: String): ByteArray? {
        val stringString = TWStringCreateWithUTF8Bytes(string)
        val result = TWBase58Decode(stringString).readTwBytes()
        TWStringDelete(stringString)
        return result
    }

    // ......
}

Definition of new readTwBytes:

internal fun COpaquePointer?.readTwBytes(): ByteArray? =
    this?.let {
        val result = TWDataBytes(it)?.readBytes(TWDataSize(it).toInt())
        TWDataDelete(it)
        result
    }