refactor(mobile): cleanup iOS image loading pipeline (#27672)

* refactor: replace DispatchQueue + DispatchSemaphore with OperationQueue for image processing

* implement RequestRegistry and UnfairLock for managing cancellable requests

* implement requests registry for local and remote image processing

* remove Cancellable protocol and cancel method from request registry

* refactor: introduce ImageRequest base class with unified cancellation and finish helpers

* refactor: add get method to RequestRegistry and streamline request removal in image processing

* add guard to cancel to prevent double onCancel calls

* fix duplicate code merge issue

* refactor(ios): enhance finish method to return callback status

* remove unfitting methods form ImageRequest.swift and fix memory issue

* revert bad merge

* refactor(ios): resolve cancellation issues

* refactor(ios): streamline image request completion handling

* add return statements

* refactor(ios): simplify image request cancellation and registry handling

---------

Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/ios/Runner/Images/RemoteImagesImpl.swift

@@ -3,27 +3,24 @@ import Flutter
 import MobileCoreServices
 import Photos
 
-class RemoteImageRequest {
-  weak var task: URLSessionDataTask?
+final class RemoteImageRequest: ImageRequest {
+  var task: URLSessionDataTask?
   let id: Int64
-  var isCancelled = false
-  let completion: (Result<[String: Int64]?, any Error>) -> Void
 
-  init(id: Int64, task: URLSessionDataTask, completion: @escaping (Result<[String: Int64]?, any Error>) -> Void) {
+  init(id: Int64, completion: @escaping @Sendable (Result<[String: Int64]?, any Error>) -> Void) {
     self.id = id
-    self.task = task
-    self.completion = completion
+    super.init(completion: completion)
   }
 
-  func cancel() {
-    isCancelled = true
+  override func cancel() {
+    super.cancel()
     task?.cancel()
   }
 }
 
 class RemoteImageApiImpl: NSObject, RemoteImageApi {
   private static let registry = RequestRegistry<RemoteImageRequest>()
-  private static var rgbaFormat = vImage_CGImageFormat(
+  private static let rgbaFormat = vImage_CGImageFormat(
     bitsPerComponent: 8,
     bitsPerPixel: 32,
     colorSpace: CGColorSpaceCreateDeviceRGB(),
@@ -41,62 +38,58 @@ class RemoteImageApiImpl: NSObject, RemoteImageApi {
     var urlRequest = URLRequest(url: URL(string: url)!)
     urlRequest.cachePolicy = .returnCacheDataElseLoad
 
+    let request = RemoteImageRequest(id: requestId, completion: completion)
+
     let task = URLSessionManager.shared.session.dataTask(with: urlRequest) { data, response, error in
-      Self.handleCompletion(requestId: requestId, encoded: preferEncoded, data: data, response: response, error: error)
+      Self.handleCompletion(request: request, encoded: preferEncoded, data: data, response: response, error: error)
     }
 
-    let request = RemoteImageRequest(id: requestId, task: task, completion: completion)
-
+    request.task = task
     Self.registry.add(requestId: requestId, request: request)
-
     task.resume()
   }
 
-  private static func handleCompletion(requestId: Int64, encoded: Bool, data: Data?, response: URLResponse?, error: Error?) {
-    guard let request = registry.remove(requestId: requestId) else {
-      return
-    }
-
-    if let error = error {
-      if request.isCancelled || (error as NSError).code == NSURLErrorCancelled {
-        return request.completion(ImageProcessing.cancelledResult)
-      }
-      return request.completion(.failure(error))
-    }
-
+  private static func handleCompletion(request: RemoteImageRequest, encoded: Bool, data: Data?, response: URLResponse?, error: Error?) {
     if request.isCancelled {
       return request.completion(ImageProcessing.cancelledResult)
     }
 
+    if let error = error {
+      registry.remove(requestId: request.id)
+      return request.completion(.failure(error))
+    }
+
     guard let data = data else {
+      registry.remove(requestId: request.id)
       return request.completion(.failure(PigeonError(code: "", message: "No data received", details: nil)))
     }
 
+    if encoded {
+      let length = data.count
+      let pointer = malloc(length)!
+      data.copyBytes(to: pointer.assumingMemoryBound(to: UInt8.self), count: length)
+
+      if request.isCancelled {
+        free(pointer)
+        return request.completion(ImageProcessing.cancelledResult)
+      }
+
+      registry.remove(requestId: request.id)
+      return request.completion(
+        .success([
+          "pointer": Int64(Int(bitPattern: pointer)),
+          "length": Int64(length),
+        ]))
+    }
+
     ImageProcessing.queue.addOperation {
       if request.isCancelled {
         return request.completion(ImageProcessing.cancelledResult)
       }
 
-      // Return raw encoded bytes when requested (for animated images)
-      if encoded {
-        let length = data.count
-        let pointer = malloc(length)!
-        data.copyBytes(to: pointer.assumingMemoryBound(to: UInt8.self), count: length)
-
-        if request.isCancelled {
-          free(pointer)
-          return request.completion(ImageProcessing.cancelledResult)
-        }
-
-        return request.completion(
-          .success([
-            "pointer": Int64(Int(bitPattern: pointer)),
-            "length": Int64(length),
-          ]))
-      }
-
       guard let imageSource = CGImageSourceCreateWithData(data as CFData, nil),
             let cgImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, decodeOptions) else {
+        registry.remove(requestId: request.id)
         return request.completion(.failure(PigeonError(code: "", message: "Failed to decode image for request", details: nil)))
       }
 
@@ -112,14 +105,16 @@ class RemoteImageApiImpl: NSObject, RemoteImageApi {
           return request.completion(ImageProcessing.cancelledResult)
         }
 
-        request.completion(
-          .success([
-            "pointer": Int64(Int(bitPattern: buffer.data)),
-            "width": Int64(buffer.width),
-            "height": Int64(buffer.height),
-            "rowBytes": Int64(buffer.rowBytes),
-          ]))
+        registry.remove(requestId: request.id)
+        return request.completion(
+                 .success([
+                   "pointer": Int64(Int(bitPattern: buffer.data)),
+                   "width": Int64(buffer.width),
+                   "height": Int64(buffer.height),
+                   "rowBytes": Int64(buffer.rowBytes),
+                 ]))
       } catch {
+        registry.remove(requestId: request.id)
         return request.completion(.failure(PigeonError(code: "", message: "Failed to convert image for request: \(error)", details: nil)))
       }
     }