*CAREFUL* Your persisted values will be lost when running in the Background on iOS

This is a great library for securily storing values, but it currently has a problem that might cause a lot of headaches to developers, specially if you already have an app running and add the Background Fetch capability into the app and start using it with libraries like react-native-background-fetch and react-native-background-timer both of which will execute operations in the background (e.g: when the phone is locked)

If your background processes interact with the Keychain, you’ll completely loose those values if you try to update them when the app is running in the background. The reason for that is because the default keychain item accessibility is that items are only accessibible when the phone is unlocked, and this library currently uses the default accessibility when you pass your key/value pair to setItem. So when you call setItem in the background, the library will first delete the existing value as can be seen here and then it’ll try to write the new value, but that’ll fail since it’s not using the proper accessibility level.

There’s a PR already opened here which increases the functionality of the library by allowing us as developers to customize the accessibility level to whatever we want. I think the maintainers should consider accepting the PR and releasing a new official version, specially considering the popularity of this library and also the impact that this behavior can silently cause in apps, which is very tricky to reproduce when you consider how background fetches are executed by iOS.

If the PR isn’t in the essense of how the maintainers believe the library should work, I think we should at least have a warning to this behavior added to the README section to prevent people from running into this issue in the future.

[wjeffersontpadua]

@jkelley79 I believe I’ve used react-native-background-timer to achieve that

[jkelley79]

@wjeffersontpadua - I setup a timeout, locked the phone but the callback is not fired until I unlock the phone and/or relaunch the app. Seems like you would need a way to trigger the app to run in the background while the phone is locked to reproduce.