How to allocate -> send -> receive -> cast -> deallocate UnsafeRawPointer from extension to app?

Question

I am new in UnsafeRawPointer. As I got I need to allocate unsafe memory in my extension and send pointer to my app where has to cast and release it. Below is a sketch of what I want to do. I'd like to send a string message from Safari extension and receive it in app by CFNotificationCenterGetDarwinNotifyCenter, how to do it?

let center = CFNotificationCenterGetDarwinNotifyCenter()

CFNotificationCenterAddObserver(center, nil, { (_, observer, name, message, _) -> Void in
    //message as String???             
}, Self.action, nil, .deliverImmediately)

var message = "some text"
CFNotificationCenterPostNotification(center, .init(action), message, nil, true)

Main questions?

• What type use to send String?
• How to allocate memory right?
• How to cast it to String in observer?
• How to deallocate memory right?

Northernmost

If the extension runs as a separate process then this is impossible: Memory allocated in one process is not available in a different process. – Alysa

Sound strange I see CFNotificationCenterGetDarwinNotifyCenter manage it. – Northernmost

Compare developer.apple.com/documentation/corefoundation/…: if center is a Darwin notification center then object and userInfo are ignored. – Alysa

How max length a message name? – Northernmost

I have no idea ... – Alysa

I guess I have to use combine UserDefaults and CFNotificationCenterGetDarwinNotifyCenter to send some long text? – Northernmost

Compare https://mcmap.net/q/832871/-send-message-from-ios-today-widget-to-app. – Alysa

Thanks for point out that object and userInfo are ignored. I missed it. Why use UnsafeRawPointer in same process? – Northernmost

Here is an example where the raw pointer is used to pass a pointer to a class instance to the callback function. – Alysa

I see but I can't imagine a situation why it is necessary since class it is reference type? – Northernmost

When I call some method with class type parameter I send a pointer. – Northernmost

CFNotificationCenterPostNotification is actually a C function, and the callback is also a pure C function. C knows nothing about Swift types or instance pointers. That's why the object parameter is a UnsafeRawPointer (the Swift equivalent of void *). – Alysa

Awesome, I got it now, thanks. – Northernmost

I add https://mcmap.net/q/815360/-how-to-properly-use-cfnotificationcenteraddobserver-in-swift-for-ios to help guys to get the goal quickly. The question is closed by me thanks @MartinR. – Northernmost

Answer 1

Thanks @MartinR, I got all answers on my questions.

We can't send an object though CFNotificationCenterPostNotification so we need to use Darwin and UserDefaults(suitename:) combination.

Schema

1. Add the CFNotificationCenterAddObserver observer in the app code
2. Save sending object in UserDefaults(suitename:)
3. Send the didObjectChanged notification through CFNotificationCenterPostNotification code
4. Catch didObjectChanged notification in CFNotificationCallback in the app code
5. Read sending object from UserDefaults(suitename:)

Off-topic

Question Why do we use UnsafeRawPointer? sample

Answer CFNotificationCenterPostNotification is actually a C function, and the callback is also a pure C function. C knows nothing about Swift types or instance pointers. That's why the object parameter is a UnsafeRawPointer (the Swift equivalent of void *).

Northernmost

You should summarize the contents of the comments in your answer. Comments are ephemeral and can be deleted at any time. – Alysa

I hope I added enough info. – Northernmost