fix: isolate ReplayKit capture state

apps/ios/Sources/Screen/ScreenRecordService.swift

@@ -6,6 +6,23 @@ final class ScreenRecordService {
         let value: T
     }
 
+    private final class CaptureState: @unchecked Sendable {
+        private let lock = NSLock()
+        var writer: AVAssetWriter?
+        var videoInput: AVAssetWriterInput?
+        var audioInput: AVAssetWriterInput?
+        var started = false
+        var sawVideo = false
+        var lastVideoTime: CMTime?
+        var handlerError: Error?
+
+        func withLock<T>(_ body: (CaptureState) -> T) -> T {
+            self.lock.lock()
+            defer { lock.unlock() }
+            return body(self)
+        }
+    }
+
     enum ScreenRecordError: LocalizedError {
         case invalidScreenIndex(Int)
         case captureFailed(String)
@@ -50,31 +67,14 @@ final class ScreenRecordService {
         }()
         try? FileManager.default.removeItem(at: outURL)
 
-        var writer: AVAssetWriter?
-        var videoInput: AVAssetWriterInput?
-        var audioInput: AVAssetWriterInput?
-        var started = false
-        var sawVideo = false
-        var lastVideoTime: CMTime?
-        var handlerError: Error?
-        let stateLock = NSLock()
-
-        func withStateLock<T>(_ body: () -> T) -> T {
-            stateLock.lock()
-            defer { stateLock.unlock() }
-            return body()
-        }
-
-        func setHandlerError(_ error: Error) {
-            withStateLock {
-                if handlerError == nil { handlerError = error }
-            }
-        }
+        let state = CaptureState()
 
         try await withCheckedThrowingContinuation { (cont: CheckedContinuation<Void, Error>) in
             let handler: @Sendable (CMSampleBuffer, RPSampleBufferType, Error?) -> Void = { sample, type, error in
                 if let error {
-                    setHandlerError(error)
+                    state.withLock { state in
+                        if state.handlerError == nil { state.handlerError = error }
+                    }
                     return
                 }
                 guard CMSampleBufferDataIsReady(sample) else { return }
@@ -82,8 +82,8 @@ final class ScreenRecordService {
                 switch type {
                 case .video:
                     let pts = CMSampleBufferGetPresentationTimeStamp(sample)
-                    let shouldSkip = withStateLock {
-                        if let lastVideoTime {
+                    let shouldSkip = state.withLock { state in
+                        if let lastVideoTime = state.lastVideoTime {
                             let delta = CMTimeSubtract(pts, lastVideoTime)
                             return delta.seconds < (1.0 / fpsValue)
                         }
@@ -91,9 +91,13 @@ final class ScreenRecordService {
                     }
                     if shouldSkip { return }
 
-                    if withStateLock({ writer == nil }) {
+                    if state.withLock({ $0.writer == nil }) {
                         guard let imageBuffer = CMSampleBufferGetImageBuffer(sample) else {
-                            setHandlerError(ScreenRecordError.captureFailed("Missing image buffer"))
+                            state.withLock { state in
+                                if state.handlerError == nil {
+                                    state.handlerError = ScreenRecordError.captureFailed("Missing image buffer")
+                                }
+                            }
                             return
                         }
                         let width = CVPixelBufferGetWidth(imageBuffer)
@@ -117,8 +121,8 @@ final class ScreenRecordService {
                                 aInput.expectsMediaDataInRealTime = true
                                 if w.canAdd(aInput) {
                                     w.add(aInput)
-                                    withStateLock {
-                                        audioInput = aInput
+                                    state.withLock { state in
+                                        state.audioInput = aInput
                                     }
                                 }
                             }
@@ -128,36 +132,43 @@ final class ScreenRecordService {
                                     .writeFailed(w.error?.localizedDescription ?? "Failed to start writer")
                             }
                             w.startSession(atSourceTime: pts)
-                            withStateLock {
-                                writer = w
-                                videoInput = vInput
-                                started = true
+                            state.withLock { state in
+                                state.writer = w
+                                state.videoInput = vInput
+                                state.started = true
                             }
                         } catch {
-                            setHandlerError(error)
+                            state.withLock { state in
+                                if state.handlerError == nil { state.handlerError = error }
+                            }
                             return
                         }
                     }
 
-                    let vInput = withStateLock { videoInput }
-                    let isStarted = withStateLock { started }
+                    let vInput = state.withLock { $0.videoInput }
+                    let isStarted = state.withLock { $0.started }
                     guard let vInput, isStarted else { return }
                     if vInput.isReadyForMoreMediaData {
                         if vInput.append(sample) {
-                            withStateLock {
-                                sawVideo = true
-                                lastVideoTime = pts
+                            state.withLock { state in
+                                state.sawVideo = true
+                                state.lastVideoTime = pts
                             }
                         } else {
-                            if let err = withStateLock({ writer?.error }) {
-                                setHandlerError(ScreenRecordError.writeFailed(err.localizedDescription))
+                            let err = state.withLock { $0.writer?.error }
+                            if let err {
+                                state.withLock { state in
+                                    if state.handlerError == nil {
+                                        state.handlerError = ScreenRecordError.writeFailed(err.localizedDescription)
+                                    }
+                                }
                             }
                         }
                     }
 
                 case .audioApp, .audioMic:
-                    let aInput = withStateLock { audioInput }
-                    let isStarted = withStateLock { started }
+                    let aInput = state.withLock { $0.audioInput }
+                    let isStarted = state.withLock { $0.started }
                     guard includeAudio, let aInput, isStarted else { return }
                     if aInput.isReadyForMoreMediaData {
                         _ = aInput.append(sample)
@@ -173,9 +184,10 @@ final class ScreenRecordService {
             }
 
             Task { @MainActor in
-                let recorder = RPScreenRecorder.shared()
-                recorder.isMicrophoneEnabled = includeAudio
-                recorder.startCapture(handler: handler, completionHandler: completion)
+                self.startCapture(
+                    includeAudio: includeAudio,
+                    handler: handler,
+                    completion: completion)
             }
         }
 
@@ -183,18 +195,17 @@ final class ScreenRecordService {
 
         let stopError = await withCheckedContinuation { cont in
             Task { @MainActor in
-                let recorder = RPScreenRecorder.shared()
-                recorder.stopCapture { error in cont.resume(returning: error) }
+                self.stopCapture { error in cont.resume(returning: error) }
             }
         }
         if let stopError { throw stopError }
 
-        let handlerErrorSnapshot = withStateLock { handlerError }
+        let handlerErrorSnapshot = state.withLock { $0.handlerError }
         if let handlerErrorSnapshot { throw handlerErrorSnapshot }
-        let writerSnapshot = withStateLock { writer }
-        let videoInputSnapshot = withStateLock { videoInput }
-        let audioInputSnapshot = withStateLock { audioInput }
-        let sawVideoSnapshot = withStateLock { sawVideo }
+        let writerSnapshot = state.withLock { $0.writer }
+        let videoInputSnapshot = state.withLock { $0.videoInput }
+        let audioInputSnapshot = state.withLock { $0.audioInput }
+        let sawVideoSnapshot = state.withLock { $0.sawVideo }
         guard let writerSnapshot, let videoInputSnapshot, sawVideoSnapshot else {
             throw ScreenRecordError.captureFailed("No frames captured")
         }
@@ -219,6 +230,22 @@ final class ScreenRecordService {
         return outURL.path
     }
 
+    @MainActor
+    private func startCapture(
+        includeAudio: Bool,
+        handler: @escaping (CMSampleBuffer, RPSampleBufferType, Error?) -> Void,
+        completion: @escaping (Error?) -> Void)
+    {
+        let recorder = RPScreenRecorder.shared()
+        recorder.isMicrophoneEnabled = includeAudio
+        recorder.startCapture(handler: handler, completionHandler: completion)
+    }
+
+    @MainActor
+    private func stopCapture(_ completion: @escaping (Error?) -> Void) {
+        RPScreenRecorder.shared().stopCapture(completionHandler: completion)
+    }
+
     private nonisolated static func clampDurationMs(_ ms: Int?) -> Int {
         let v = ms ?? 10000
         return min(60000, max(250, v))