Synchronizing files using file provider extensions

At a glance

Project structure

Source bundle/
├── FruitBasket-iOS/
│   ├── FruitBasketApp.swift
│   ├── SettingsView.swift
│   ├── AddDomain.swift
│   └── ContentView.swift
├── FruitBasket/
│   └── AppDelegate.swift
├── Common/
│   ├── AccountService.swift
│   ├── DomainService.swift
│   ├── EnumerationView.swift
│   └── ContentBasedChunkStore.swift
├── Provider/
│   └── main.swift
├── Action/
│   └── ConflictViewController.swift
└── Server/
    └── ItemDatabase.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C/Objective-C header, Swift.
• The verified tree contains 20 project/configuration file(s) and 182 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["FruitBasket-iOS"]
    V2["FruitBasket"]
    Boundary["FileProvider APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary

Reference code

FruitBasket-iOS/FruitBasketApp.swift:10 — architecture anchor

@main
struct FruitBasketApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView().navigationTitle("Domains")
        }
    }
}

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    Account *-- String : identifier
    Account *-- String : secret
    Account *-- String : displayName
    Account o-- Entry : rootItem

Ownership evidence

Common/AccountService.swift:15 — stored dependency or nearest verified ownership anchor

    public struct Account: Codable {
        public let identifier: String
        // ...
    }

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

Action/AuthenticationViewController.swift:42 — representative execution boundary

        Task {
            // ...
            let conn = DomainConnection(domainIdentifier: self.actionViewController.domain.identifier.rawValue, secret: "",
                                              hostname: UserDefaults.sharedContainerDefaults.hostname, port: self.port)
            // ...
        }

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

Common/ContentBasedChunkStore.swift:11 — representative type boundary

public protocol ContentBasedChunkStore {
    func chunkExists(sha256OfChunk: Data) -> Bool
    func createChunk(sha256OfChunk: Data, chunkData: Data) throws
    func retrieveChunk(sha256OfChunk: Data) throws -> Data?

    func close()
}

The source explicitly defines local protocol relationships: AuthenticationViewController → ConcreteActionViewController, ConflictViewController → ConcreteActionViewController, InfoParameter → JSONParameter, ListAccountParameter → JSONParameter, CreateAccountParameter → JSONParameter, RemoveAccountParameter → JSONParameter.

Access control

Reference code

Action/ActionViewController.swift:19 — representative boundary

public class ActionViewController: FPUIActionExtensionViewController {
    private let logger = Logger(subsystem: "com.example.apple-samplecode.FruitBasket", category: "action")
    // ...
}

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Main application flow

sequenceDiagram
    participant ConflictViewController
    participant MainActor
    participant FileManager
    participant service
    ConflictViewController->>ConflictViewController: getUserVisibleURL()
    ConflictViewController->>MainActor: Run UI-isolated work
    ConflictViewController->>FileManager: FileManager()
    ConflictViewController->>service: fileProviderConnection()

Reference code

Action/ConflictViewController.swift:97 — withServiceConnection()

    nonisolated
    internal func withServiceConnection() async throws -> FruitBasketServiceV1 {
        let url = try await self.manager.getUserVisibleURL(for: self.itemIdentifier)
        await MainActor.run {
            self.itemURL = url
        }

        let services = try await FileManager().fileProviderServicesForItem(at: url)
        guard let service = services[fruitBasketServiceName] else {
            self.logger.error("couldn't get service, fruitBasketServiceName not present")
            throw NSFileProviderError(.providerNotFound)
        }
        let connection: NSXPCConnection
        connection = try await service.fileProviderConnection()
        connection.remoteObjectInterface = fruitBasketServiceInterface
        connection.interruptionHandler = {
            self.logger.error("service connection interrupted")
        }
        connection.resume()
        guard let proxy = connection.remoteObjectProxy as? FruitBasketServiceV1 else {
            throw NSFileProviderError(.serverUnreachable)
         }
        return proxy
     }

Naming conventions

• Types: App: FruitBasketApp; Controller: ActionViewController, AuthenticationViewController, ConcreteActionViewController, ConflictViewController, EditDomainWindowController; Delegate: AppDelegate; Observer: DomainObserver; Service: AccountService, DomainService; Store: ContentBasedChunkStore, LocalContentBasedChunkStore; Transformer: EditDateValueTransformer, MillisecondTransformer, PercentageTransformer; View: BlockedProcessesEditorView, ContentView, DomainDetailView, EnumerationView, RemoteAccountView.
• Protocols: ContentBasedChunkStore, ConcreteActionViewController, JSONParameter, FruitBasketServiceV1, XAttrGettable, DispatchBackend, BackendCallRegistration, XAttrSettable.
• Methods: notify, serverChangeReceived, signalItems, setupDomainPipe, setupDomainPipeAsync, handleDomainPipeError, itemsChanged, updateItemCount.
• Files: FruitBasket-iOS/FruitBasketApp.swift, FruitBasket/AppDelegate.swift, Common/AccountService.swift, Common/DomainService.swift, Common/EnumerationView.swift, FruitBasket-iOS/SettingsView.swift.

Architecture takeaways

• FruitBasketApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Common, FileProvider, SwiftUI, SQLite through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation