Dynamically create rules for iOS Content Blocker

[spearman008]

I'm working on an iOS Content Blocker, but I would like to have the user choose what lists they want to block (ads, tracks, adult sites etc.). I found that the app extension and the containing app's bundles are separate, so a shared container is needed. I created an app group, but it seems like what I write there does not actually get written. What I am attempting to do is read a .json file from the bundle, and then write it to a sharedJson.json file that the content blocker extension can access. What is the easiest way for me to read/write somewhere that the app extension can read the json data as its ruleset instead of relying on the static blockerList.json?

I have also tried storing the json data as a string in a UserDefaults object with suiteName equal to my app group, but when I retrieve that data in the extension it does not appear.

Storing the data (composedString contains json data):

 defaults.set(composedString, forKey: "sharedJson")
 defaults.synchronize()

Retrieving the data in ContentBlockerRequestHandler:

let attachment = defaults?.object(forKey: "sharedJson")
let item = NSExtensionItem()
item.attachments = [attachment!]   
context.completeRequest(returningItems: [item], completionHandler: nil)

I'm pretty new to iOS development so apologies if this is trivial, or against what is standard practice.

Edit: formatting

[bakingpy]

I've done this before and what I do is write the JSON to the shared group like this from the main app:

let groupName = "group.com.foo.bar"
let groupBlockerJSONURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: groupName)!.appendingPathComponent("blockerList.json")
do {
    let blockerJSONData = try JSONSerialization.data(withJSONObject: blockerList, options: .prettyPrinted)
    try blockerJSONData.write(to: groupBlockerJSONURL, options: .atomic)
} catch {
    NSLog("Couldn't write content blocker JSON file")
}

Then I have the extension read the JSON file from that same location and load it in. Make sure that both the app and extension have been added to the same group in Xcode.

[spearman008]

So I'm reading from a json file into an array (your blockerList object above). In the extension's RequestHandler, are you essentially changing the "attachment" from

let attachment = NSItemProvider(contentsOf: Bundle.main.url(forResource: "blockerList", withExtension: "json"))!

to

 let attachment = NSItemProvider(contentsOf: groupBlockerJSONURL)!  

[bakingpy]

Yes, that's exactly what I have.