feat(helper): replace AudioObject IPC with XPC helper service#4
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feat(helper): replace AudioObject IPC with XPC helper service#4
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Also adds VS Code launch configurations for AppFadersHelper debug/release.
Add four new error cases for XPC communication failures: - helperNotRunning: helper service not available - connectionFailed: XPC connection establishment failed - connectionInterrupted: XPC connection was interrupted - remoteError: helper returned an error
Duplicate AppFadersHostProtocol in host target for NSXPCInterface. Must match helper's definition exactly for XPC to work.
Replace AudioObject property IPC with XPC communication to helper service. - connect() now async, connects to mach service (no deviceID param) - setAppVolume/getAppVolume now async throws - Uses withCheckedThrowingContinuation for XPC reply handling - Handles connection invalidation and interruption - Removes all CoreAudio/AudioObject code
Adapt orchestrator to async XPC-based DriverBridge: - getVolume now async throws - setVolume now async with internal error handling - restoreVolumes and handleAppEvent now async - connect() no longer takes deviceID parameter
Add helper installation before driver: - Build helper with swift build - Create /Library/Application Support/AppFaders/ - Copy helper binary with proper permissions - Install LaunchAgent plist to /Library/LaunchAgents/ - Load LaunchAgent with launchctl
Add helper cleanup after driver removal: - Unload LaunchAgent with launchctl - Remove LaunchAgent plist from /Library/LaunchAgents/ - Remove helper binary from support directory - Remove support directory if empty - Handle missing files gracefully
- Convert all tests to async - Remove CoreAudio import and connect(deviceID:) calls - Update #expect blocks to use await - Rename deviceNotFound test to helperNotRunning - Delete orphaned VolumeStoreTests (VolumeStore moved to helper)
Manual test procedure for verifying XPC communication: - Install/uninstall steps - Log stream commands for driver and helper - Volume set/get verification - Driver cache verification - Troubleshooting section - Success criteria checklist
Driver was failing to load because: 1. Helper was a LaunchAgent (user session) but driver runs in system context (Core-Audio-Driver-Service.helper) 2. XPC calls during driver init blocked for 30s causing timeout Changes: - Switch helper from LaunchAgent to LaunchDaemon - Use launchctl bootstrap/bootout for system domain - Defer initial cache refresh to background queue
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Context
The original IPC approach using custom AudioObject properties failed because coreaudiod blocks custom property writes before they reach the driver. Solution follows the BackgroundMusic pattern (BGMXPCHelper) and Apple QA1811: a separate helper process that both host app and driver connect to via XPC.
Key discoveries during implementation:
Core-Audio-Driver-Service.helper)Changes Made
New Target: AppFadersHelper
Host App
Driver
AudioServerPlugIn_MachServicesto Info.plistScripts
Testing Notes
Integration test verified (
Docs/xpc-integration-test.md):All 30 unit tests pass.