Creating an audio device driver

At a glance

Project structure

Source bundle/
├── Shared/
│   ├── SimpleAudioApp.swift
│   ├── SimpleAudioViewModel.swift
│   ├── SimpleAudioUserClient.mm
│   ├── SimpleAudioView.swift
│   ├── SimpleAudioUserClient.h
│   └── SimpleAudioDriverKeys.h
├── SimpleAudioDriverExtension/
│   ├── SimpleAudioDriverUserClient.cpp
│   ├── SimpleAudioDevice.cpp
│   ├── SimpleAudioDriver.cpp
│   ├── SimpleAudioDriver.iig
│   ├── SimpleAudioDevice.iig
│   ├── SimpleAudioDriverUserClient.iig
│   └── SimpleAudioDriverKeys.h
├── Configuration/
│   └── SampleCode.xcconfig
└── SimpleAudioDriverExtension.xcodeproj/
    └── .xcodesamplecode.plist

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C++, C/Objective-C header, Objective-C++, Swift.
• The verified tree contains 7 project/configuration file(s) and 11 source declaration(s).

Overall architecture

flowchart LR
    N1["SimpleAudioApp"]
    N2["SimpleAudioView"]
    N3["SimpleAudioViewModel"]
    N4["SimpleAudioUserClient"]
    N5["DriverKit / AudioDriverKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

Shared/SimpleAudioApp.swift:10 — architecture anchor

@main
struct SimpleAudioApp: App {
    var body: some Scene {
        WindowGroup {
            SimpleAudioView()
        }
    }
}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into AudioDriverKit.

Ownership and state

classDiagram
    SimpleAudioViewModel o-- State : state
    SimpleAudioViewModel *-- String : dextIdentifier
    SimpleAudioUserClient o-- IONotificationPortRef : mIOKitNotificationPort
    SimpleAudioUserClient o-- io_object_t : ioObject

Ownership evidence

Shared/SimpleAudioViewModel.swift:78 — stored dependency or nearest verified ownership anchor

class SimpleAudioViewModel: NSObject {
    // ...
    @Published private var state: SimpleAudioDriverLoadingStateMachine.State = .unloaded
    // ...
}

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.

Class and protocol design

SimpleAudioDriverExtension/SimpleAudioDriver.iig:18 — DriverKit service boundary

class SimpleAudioDriver: public IOUserAudioDriver
{
public:
    virtual bool init() override;
    virtual void free() override;
    virtual kern_return_t Start(IOService* provider) override;
    virtual kern_return_t Stop(IOService* provider) override;
    virtual kern_return_t NewUserClient(uint32_t in_type,
                                        IOUserClient** out_user_client) override;
    virtual kern_return_t StartDevice(IOUserAudioObjectID in_object_id,
                                      IOUserAudioStartStopFlags in_flags) override;
    virtual kern_return_t StopDevice(IOUserAudioObjectID in_object_id,
                                     IOUserAudioStartStopFlags in_flags) override;
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

Shared/SimpleAudioUserClient.mm:13 — representative boundary

@interface SimpleAudioUserClient()
@property IONotificationPortRef mIOKitNotificationPort;
@property io_object_t ioObject;
@property io_connect_t ioConnection;
@end

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

Naming conventions

• Types: App: SimpleAudioApp; Client: SimpleAudioUserClient; View: SimpleAudioView; ViewModel: SimpleAudioViewModel.
• Protocols: no local protocol declaration in the scanned source.
• Methods: process, activateMyDext, activateExtension, deactivateExtension, request, requestNeedsUserApproval, checkDeviceCustomProperties, open.
• Files: Shared/SimpleAudioApp.swift, Shared/SimpleAudioViewModel.swift, Shared/SimpleAudioUserClient.mm, Shared/SimpleAudioView.swift, Shared/SimpleAudioUserClient.h.

Architecture takeaways

• SimpleAudioApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches DriverKit, AudioDriverKit, CoreAudio, SwiftUI 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.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation