when we have only two elements I think it's better to use std::pair:

• std::tuple is built to handle more elements which means could be slower/worse in terms of memory used
• using member values first and second seems more straightforward than calling methods
• when see a pair, I immediately know that there are exactly two items involved, with std::tuple it could be any number

But I feel like like those are more personal preferences so if you have a different opinion std::tuple also makes sense to me

in this case, you have to also call this->persistCryptoModule();

I think we could deprecate generateAndGetPrekeys to avoid misuse in the future

If this the right condition? In validateAndUploadPrekeys, we appear to check has_value.

Nit: I would add another newline here, since the contentPrekeySignature is more associated with the contentPrekey than the other two variables

Yes, according to cppreference:

When an object of type optional<T> is contextually converted to bool, the conversion returns true if the object contains a value and false if it does not contain a value.

This also explicitly says that explicit operator bool() const and bool has_value() const are synonymous: https://en.cppreference.com/w/cpp/utility/optional/operator_bool

I think you ar right. We should call persistCryptoAccount() after validation without any condition.

I've just realized that there is another bug in this function. Since you've already modified this function, could you put those lines here?

if(this->cryptoModule == nullptr) {
    this->jsInvoker_->invokeAsync([=, &innerRt]() {
        promise->reject("user has not been initialized");
    });
    return;
}

Basically in this function we don't check if cryptoModule has been initialized and we should early reject and return in case it hasn't been.

There is too much indentation here. In this line I think you should reject the promise and return early. Then you could remove else wrapping around the try ... catch.

Technically correct, but we don't use this style of if statements in the codebase. I think you should just assign contentPrekey = this->cryptoModule->validatePrekey() right away and then conditionally perform other assignments if contentPrekey doesn't have value.

This task should be prioritized to avoid such mistakes in future.