iOS FlutterTextureRegistry should be a proxy, not the engine itself (#37666)

* feat: add texture registry relay.

* fix: add test.

* fix: format

* fix: add comment.

* fix: remove useless import.

* fix: remove

* fix: file name order.

* fix.

* add test for retain cycle.

* fix compile

* Add comments.

* remove relay.

* add FlutterTextureRegistryRelay in gn

* add golden files.

* add

* add comments.

Author: endless7

ci/licenses_golden/licenses_flutter

@@ -2519,6 +2519,9 @@ ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextI
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPluginTest.mm + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.mm + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelayTest.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUIPressProxy.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUIPressProxy.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUmbrellaImport.m + ../../../flutter/LICENSE
@@ -5000,6 +5003,9 @@ FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInp
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPluginTest.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.h
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelayTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUIPressProxy.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUIPressProxy.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterUmbrellaImport.m

shell/platform/darwin/ios/BUILD.gn

@@ -106,6 +106,8 @@ source_set("flutter_framework_source") {
     "framework/Source/FlutterSemanticsScrollView.mm",
     "framework/Source/FlutterSpellCheckPlugin.h",
     "framework/Source/FlutterSpellCheckPlugin.mm",
+    "framework/Source/FlutterTextureRegistryRelay.h",
+    "framework/Source/FlutterTextureRegistryRelay.mm",
     "framework/Source/FlutterUIPressProxy.h",
     "framework/Source/FlutterUIPressProxy.mm",
     "framework/Source/FlutterUndoManagerDelegate.h",
@@ -282,6 +284,7 @@ shared_library("ios_test_flutter") {
     "framework/Source/FlutterRestorationPluginTest.mm",
     "framework/Source/FlutterSpellCheckPluginTest.mm",
     "framework/Source/FlutterTextInputPluginTest.mm",
+    "framework/Source/FlutterTextureRegistryRelayTest.mm",
     "framework/Source/FlutterUndoManagerPluginTest.mm",
     "framework/Source/FlutterViewControllerTest.mm",
     "framework/Source/SemanticsObjectTest.mm",

shell/platform/darwin/ios/framework/Headers/FlutterEngine.h

@@ -56,7 +56,7 @@ extern NSString* const FlutterDefaultInitialRoute;
  * One of these methods must be invoked before calling `-setViewController:`.
  */
 FLUTTER_DARWIN_EXPORT
-@interface FlutterEngine : NSObject <FlutterTextureRegistry, FlutterPluginRegistry>
+@interface FlutterEngine : NSObject <FlutterPluginRegistry>
 
 /**
  * Default initializer for a FlutterEngine.
@@ -424,6 +424,11 @@ FLUTTER_DARWIN_EXPORT
  */
 @property(nonatomic, readonly) NSObject<FlutterBinaryMessenger>* binaryMessenger;
 
+/**
+ * The `FlutterTextureRegistry` associated with this FlutterEngine (used to register textures).
+ */
+@property(nonatomic, readonly) NSObject<FlutterTextureRegistry>* textureRegistry;
+
 /**
  * The UI Isolate ID of the engine.
  *

shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -26,6 +26,7 @@
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformPlugin.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterSpellCheckPlugin.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputDelegate.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterUndoManagerDelegate.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterUndoManagerPlugin.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h"
@@ -87,7 +88,8 @@ - (instancetype)initWithPlugin:(NSString*)pluginKey flutterEngine:(FlutterEngine
 @interface FlutterEngine () <FlutterIndirectScribbleDelegate,
                              FlutterUndoManagerDelegate,
                              FlutterTextInputDelegate,
-                             FlutterBinaryMessenger>
+                             FlutterBinaryMessenger,
+                             FlutterTextureRegistry>
 // Maintains a dictionary of plugin names that have registered with the engine.  Used by
 // FlutterEngineRegistrar to implement a FlutterPluginRegistrar.
 @property(nonatomic, readonly) NSMutableDictionary* pluginPublications;
@@ -138,6 +140,7 @@ @implementation FlutterEngine {
   BOOL _allowHeadlessExecution;
   BOOL _restorationEnabled;
   FlutterBinaryMessengerRelay* _binaryMessenger;
+  FlutterTextureRegistryRelay* _textureRegistry;
   std::unique_ptr<flutter::ConnectionCollection> _connections;
 }
 
@@ -197,6 +200,7 @@ - (instancetype)initWithName:(NSString*)labelPrefix
   [self recreatePlatformViewController];
 
   _binaryMessenger = [[FlutterBinaryMessengerRelay alloc] initWithParent:self];
+  _textureRegistry = [[FlutterTextureRegistryRelay alloc] initWithParent:self];
   _connections.reset(new flutter::ConnectionCollection());
 
   NSNotificationCenter* center = [NSNotificationCenter defaultCenter];
@@ -261,7 +265,10 @@ - (void)dealloc {
   [_pluginPublications release];
   [_registrars release];
   _binaryMessenger.parent = nil;
+  _textureRegistry.parent = nil;
   [_binaryMessenger release];
+  [_textureRegistry release];
+  _textureRegistry = nil;
   [_isolateId release];
 
   NSNotificationCenter* center = [NSNotificationCenter defaultCenter];
@@ -1073,6 +1080,10 @@ - (void)flutterViewAccessibilityDidCall {
   return _binaryMessenger;
 }
 
+- (NSObject<FlutterTextureRegistry>*)textureRegistry {
+  return _textureRegistry;
+}
+
 // For test only. Ideally we should create a dependency injector for all dependencies and
 // remove this.
 - (void)setBinaryMessenger:(FlutterBinaryMessengerRelay*)binaryMessenger {
@@ -1333,7 +1344,7 @@ - (void)dealloc {
 }
 
 - (NSObject<FlutterTextureRegistry>*)textures {
-  return _flutterEngine;
+  return _flutterEngine.textureRegistry;
 }
 
 - (void)publish:(NSObject*)value {

shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.h

@@ -0,0 +1,24 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterMacros.h"
+#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterTexture.h"
+
+#if FLUTTER_RUNTIME_MODE == FLUTTER_RUNTIME_MODE_DEBUG
+FLUTTER_DARWIN_EXPORT
+#endif
+
+/**
+ * Wrapper around a weakly held collection of registered textures.
+ *
+ * Avoids a retain cycle between plugins and the engine.
+ */
+@interface FlutterTextureRegistryRelay : NSObject <FlutterTextureRegistry>
+
+/**
+ * A weak reference to a FlutterEngine that will be passed texture registration.
+ */
+@property(nonatomic, assign) NSObject<FlutterTextureRegistry>* parent;
+- (instancetype)initWithParent:(NSObject<FlutterTextureRegistry>*)parent;
+@end

shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.mm

@@ -0,0 +1,42 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.h"
+
+#include "flutter/fml/logging.h"
+
+@implementation FlutterTextureRegistryRelay : NSObject
+
+#pragma mark - FlutterTextureRegistry
+
+- (instancetype)initWithParent:(NSObject<FlutterTextureRegistry>*)parent {
+  if (self = [super init]) {
+    _parent = parent;
+  }
+  return self;
+}
+
+- (int64_t)registerTexture:(NSObject<FlutterTexture>*)texture {
+  if (!self.parent) {
+    FML_LOG(WARNING) << "Using on an empty registry.";
+    return 0;
+  }
+  return [self.parent registerTexture:texture];
+}
+
+- (void)textureFrameAvailable:(int64_t)textureId {
+  if (!self.parent) {
+    FML_LOG(WARNING) << "Using on an empty registry.";
+  }
+  return [self.parent textureFrameAvailable:textureId];
+}
+
+- (void)unregisterTexture:(int64_t)textureId {
+  if (!self.parent) {
+    FML_LOG(WARNING) << "Using on an empty registry.";
+  }
+  return [self.parent unregisterTexture:textureId];
+}
+
+@end

shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelayTest.mm

@@ -0,0 +1,66 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterEngine.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTextureRegistryRelay.h"
+
+#import <OCMock/OCMock.h>
+#import <XCTest/XCTest.h>
+
+#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterMacros.h"
+#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterTexture.h"
+
+FLUTTER_ASSERT_ARC
+
+@interface FlutterTextureRegistryRelayTest : XCTestCase
+@end
+
+@implementation FlutterTextureRegistryRelayTest
+
+- (void)testCreate {
+  id textureRegistry = OCMProtocolMock(@protocol(FlutterTextureRegistry));
+  FlutterTextureRegistryRelay* relay =
+      [[FlutterTextureRegistryRelay alloc] initWithParent:textureRegistry];
+  XCTAssertNotNil(relay);
+  XCTAssertEqual(textureRegistry, relay.parent);
+}
+
+- (void)testRegisterTexture {
+  id textureRegistry = OCMProtocolMock(@protocol(FlutterTextureRegistry));
+  FlutterTextureRegistryRelay* relay =
+      [[FlutterTextureRegistryRelay alloc] initWithParent:textureRegistry];
+  id texture = OCMProtocolMock(@protocol(FlutterTexture));
+  [relay registerTexture:texture];
+  OCMVerify([textureRegistry registerTexture:texture]);
+}
+
+- (void)testTextureFrameAvailable {
+  id textureRegistry = OCMProtocolMock(@protocol(FlutterTextureRegistry));
+  FlutterTextureRegistryRelay* relay =
+      [[FlutterTextureRegistryRelay alloc] initWithParent:textureRegistry];
+  [relay textureFrameAvailable:0];
+  OCMVerify([textureRegistry textureFrameAvailable:0]);
+}
+
+- (void)testUnregisterTexture {
+  id textureRegistry = OCMProtocolMock(@protocol(FlutterTextureRegistry));
+  FlutterTextureRegistryRelay* relay =
+      [[FlutterTextureRegistryRelay alloc] initWithParent:textureRegistry];
+  [relay unregisterTexture:0];
+  OCMVerify([textureRegistry unregisterTexture:0]);
+}
+
+- (void)testRetainCycle {
+  __weak FlutterEngine* weakEngine;
+  NSObject<FlutterTextureRegistry>* strongRelay;
+  @autoreleasepool {
+    id project = OCMClassMock([FlutterDartProject class]);
+    FlutterEngine* engine = [[FlutterEngine alloc] initWithName:@"foobar" project:project];
+    strongRelay = [engine textureRegistry];
+    weakEngine = engine;
+  }
+  XCTAssertNil(weakEngine);
+}
+
+@end

shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -2022,15 +2022,15 @@ - (void)cleanUpConnection:(FlutterBinaryMessengerConnection)connection {
 #pragma mark - FlutterTextureRegistry
 
 - (int64_t)registerTexture:(NSObject<FlutterTexture>*)texture {
-  return [_engine.get() registerTexture:texture];
+  return [_engine.get().textureRegistry registerTexture:texture];
 }
 
 - (void)unregisterTexture:(int64_t)textureId {
-  [_engine.get() unregisterTexture:textureId];
+  [_engine.get().textureRegistry unregisterTexture:textureId];
 }
 
 - (void)textureFrameAvailable:(int64_t)textureId {
-  [_engine.get() textureFrameAvailable:textureId];
+  [_engine.get().textureRegistry textureFrameAvailable:textureId];
 }
 
 - (NSString*)lookupKeyForAsset:(NSString*)asset {