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fix: handle exceptions when FlutterEngine is suspended during event emission
- Added exception handling in `AblyStreamsChannel` to prevent crashes when FlutterEngine is stopped. - Improved logging to notify dropped events due to engine inactivity. - Added iOS unit tests for regression and normal operation of event sinks. - Configured GitHub Actions to run iOS unit tests on macOS.
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-21
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4 files changed

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‎.github/workflows/ios_unit_tests.yml‎

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on:
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workflow_dispatch:
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pull_request:
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push:
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branches:
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- main
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jobs:
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ios-unit-tests:
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runs-on: macos-latest
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steps:
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- uses: actions/checkout@v4
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- uses: futureware-tech/simulator-action@v5
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id: ios-simulator
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- uses: subosito/flutter-action@v2
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with:
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flutter-version: '3.29'
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cache: true
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- name: Set up iOS test project
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# --skip-tests sets up the CocoaPods workspace (downloads all deps, generates
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# the ably_flutter-Unit-Tests scheme) without booting a simulator
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run: |
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cd ios
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pod lib lint ably_flutter.podspec \
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--allow-warnings \
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--skip-tests \
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--validation-dir=/tmp/ably_test_build \
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--no-clean
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- name: Run iOS unit tests
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timeout-minutes: 30
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run: |
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xcodebuild test \
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-workspace /tmp/ably_test_build/App.xcworkspace \
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-scheme ably_flutter-Unit-Tests \
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-destination 'id=${{ steps.ios-simulator.outputs.udid }}' \
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CODE_SIGNING_ALLOWED=NO

‎ios/Classes/AblyStreamsChannel.m‎

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Original file line numberDiff line numberDiff line change
@@ -66,26 +66,26 @@ - (void)setStreamHandlerFactory:(NSObject<FlutterStreamHandler> *(^)(id))factory
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[_messenger setMessageHandlerOnChannel:_name binaryMessageHandler:nil];
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return;
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}
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_streams = [NSMutableDictionary new];
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_listenerArguments = [NSMutableDictionary new];
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FlutterBinaryMessageHandler messageHandler = ^(NSData* message, FlutterBinaryReply callback) {
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FlutterMethodCall* call = [self->_codec decodeMethodCall:message];
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NSArray *methodParts = [call.method componentsSeparatedByString:@"#"];
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if (methodParts.count != 2) {
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callback(nil);
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return;
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}
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NSInteger keyValue = [methodParts.lastObject integerValue];
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if(keyValue == 0) {
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callback([self->_codec encodeErrorEnvelope:[FlutterError errorWithCode:@"error" message:[NSString stringWithFormat:@"Invalid method name: %@", call.method] details:nil]]);
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return;
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}
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NSNumber *key = [NSNumber numberWithInteger:keyValue];
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if ([methodParts.firstObject isEqualToString:@"listen"]) {
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[self listenForCall:call withKey:key usingCallback:callback andFactory:factory];
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} else if ([methodParts.firstObject isEqualToString:@"cancel"]) {
@@ -94,7 +94,7 @@ - (void)setStreamHandlerFactory:(NSObject<FlutterStreamHandler> *(^)(id))factory
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callback(nil);
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}
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};
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[_messenger setMessageHandlerOnChannel:_name binaryMessageHandler:messageHandler];
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}
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@@ -110,22 +110,25 @@ - (void) reset{
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- (void)listenForCall:(FlutterMethodCall*)call withKey:(NSNumber*)key usingCallback:(FlutterBinaryReply)callback andFactory:(NSObject<FlutterStreamHandler> *(^)(id))factory {
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AblyStreamsChannelStream *stream = [AblyStreamsChannelStream new];
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stream.sink = ^(id event) {
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NSString *name = [NSString stringWithFormat:@"%@#%@", self->_name, key];
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if (event == FlutterEndOfEventStream) {
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[self->_messenger sendOnChannel:name message:nil];
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} else if ([event isKindOfClass:[FlutterError class]]) {
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[self->_messenger sendOnChannel:name
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message:[self->_codec encodeErrorEnvelope:(FlutterError*)event]];
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} else {
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[self->_messenger sendOnChannel:name message:[self->_codec encodeSuccessEnvelope:event]];
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@try {
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NSString *name = [NSString stringWithFormat:@"%@#%@", self->_name, key];
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if (event == FlutterEndOfEventStream) {
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[self->_messenger sendOnChannel:name message:nil];
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} else if ([event isKindOfClass:[FlutterError class]]) {
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[self->_messenger sendOnChannel:name
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message:[self->_codec encodeErrorEnvelope:(FlutterError*)event]];
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} else {
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[self->_messenger sendOnChannel:name message:[self->_codec encodeSuccessEnvelope:event]];
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}
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} @catch (NSException *exception) {
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NSLog(@"AblyFlutter: Dropped event, engine not running: %@", exception.reason);
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}
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};
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stream.handler = factory(call.arguments);
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[_streams setObject:stream forKey:key];
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[_listenerArguments setObject:call.arguments forKey:key];
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[self triggerCallback:callback
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error:[stream.handler onListenWithArguments:call.arguments eventSink:stream.sink]];
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}
@@ -136,10 +139,10 @@ - (void)cancelForCall:(FlutterMethodCall*)call withKey:(NSNumber*)key usingCallb
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callback([_codec encodeErrorEnvelope:[FlutterError errorWithCode:@"error" message:@"No active stream to cancel" details:nil]]);
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return;
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}
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[_streams removeObjectForKey:key];
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[_listenerArguments removeObjectForKey:key];
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[self triggerCallback:callback error:[stream.handler onCancelWithArguments:call.arguments]];
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}
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‎ios/Tests/AblyStreamsChannelTests.m‎

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#import <XCTest/XCTest.h>
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#import <Flutter/Flutter.h>
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#import "AblyStreamsChannel.h"
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// Mock binary messenger: captures the binaryMessageHandler registered by AblyStreamsChannel,
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// and optionally throws NSInternalInconsistencyException on sendOnChannel:message: to simulate
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// a suspended/detached FlutterEngine.
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@interface MockThrowingMessenger : NSObject <FlutterBinaryMessenger>
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@property(nonatomic, copy) FlutterBinaryMessageHandler capturedHandler;
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@property(nonatomic, assign) BOOL shouldThrow;
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@property(nonatomic, assign) NSInteger sendCallCount;
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@end
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@implementation MockThrowingMessenger
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- (void)sendOnChannel:(NSString*)channel message:(NSData*)message {
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_sendCallCount++;
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if (_shouldThrow) {
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[NSException raise:NSInternalInconsistencyException
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format:@"Sending a message before the FlutterEngine has been run."];
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}
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}
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- (void)sendOnChannel:(NSString*)channel message:(NSData*)message binaryReply:(FlutterBinaryReply)callback {}
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- (FlutterBinaryMessengerConnection)setMessageHandlerOnChannel:(NSString*)channel
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binaryMessageHandler:(FlutterBinaryMessageHandler _Nullable)handler {
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_capturedHandler = handler;
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return 0;
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}
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- (FlutterBinaryMessengerConnection)setMessageHandlerOnChannel:(NSString*)channel
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binaryMessageHandler:(FlutterBinaryMessageHandler _Nullable)handler
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taskQueue:(NSObject<FlutterTaskQueue>* _Nullable)taskQueue {
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_capturedHandler = handler;
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return 0;
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}
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- (void)cleanUpConnection:(FlutterBinaryMessengerConnection)connection {}
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- (NSObject<FlutterTaskQueue>*)makeBackgroundTaskQueue { return nil; }
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@end
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// Helper stream handler that captures the eventSink passed to it during stream setup.
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@interface CapturingSinkHandler : NSObject <FlutterStreamHandler>
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@property(nonatomic, copy) FlutterEventSink capturedSink;
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@end
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@implementation CapturingSinkHandler
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- (FlutterError*)onListenWithArguments:(id)arguments eventSink:(FlutterEventSink)events {
53+
_capturedSink = events;
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return nil;
55+
}
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- (FlutterError*)onCancelWithArguments:(id)arguments { return nil; }
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@end
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@interface AblyStreamsChannelTests : XCTestCase
62+
@end
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@implementation AblyStreamsChannelTests
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// Sets up an AblyStreamsChannel with the given messenger and triggers a "listen#1" call,
67+
// which causes the channel to create a sink and pass it to the handler's onListenWithArguments:.
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// Returns the handler so tests can invoke the captured sink.
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- (CapturingSinkHandler*)setupChannelWithMessenger:(MockThrowingMessenger*)messenger {
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AblyStreamsChannel *channel = [AblyStreamsChannel
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streamsChannelWithName:@"test.channel"
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binaryMessenger:messenger
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codec:[FlutterStandardMethodCodec sharedInstance]];
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CapturingSinkHandler *handler = [CapturingSinkHandler new];
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[channel setStreamHandlerFactory:^NSObject<FlutterStreamHandler>*(id args) { return handler; }];
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// Simulate Flutter sending a "listen#1" message to open a stream.
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// Arguments must be non-nil: AblyStreamsChannel stores them in an NSMutableDictionary
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// which rejects nil values.
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NSData *listenMsg = [[FlutterStandardMethodCodec sharedInstance]
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encodeMethodCall:[FlutterMethodCall methodCallWithMethodName:@"listen#1" arguments:@{}]];
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messenger.capturedHandler(listenMsg, ^(NSData* reply){});
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return handler;
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}
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// Regression test for: NSInternalInconsistencyException crash when the FlutterEngine is
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// suspended after the app is backgrounded.
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// The sink block in AblyStreamsChannel must catch the exception instead of propagating it.
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- (void)testSinkDoesNotCrashWhenEngineNotRunning {
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MockThrowingMessenger *messenger = [MockThrowingMessenger new];
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messenger.shouldThrow = YES;
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CapturingSinkHandler *handler = [self setupChannelWithMessenger:messenger];
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XCTAssertNoThrow(handler.capturedSink(@"state-change-event"),
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@"Sink should swallow NSInternalInconsistencyException when engine is stopped");
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}
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// Verify the normal (foreground) code path still works after the fix.
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- (void)testSinkEmitsNormallyWhenEngineIsRunning {
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MockThrowingMessenger *messenger = [MockThrowingMessenger new];
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messenger.shouldThrow = NO;
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CapturingSinkHandler *handler = [self setupChannelWithMessenger:messenger];
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XCTAssertNoThrow(handler.capturedSink(@"state-change-event"));
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XCTAssertEqual(messenger.sendCallCount, 1,
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@"Messenger should be called once for a normal event emission");
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}
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@end

‎ios/ably_flutter.podspec‎

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@@ -22,12 +22,16 @@ Pod::Spec.new do |s|
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s.platform = :ios
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s.ios.deployment_target = '10.0'
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# Flutter.framework does not contain a i386 slice. Only x86_64 simulators are supported.
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# Flutter 3.x ships both arm64 and x86_64 simulator slices; no arch restriction needed.
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s.pod_target_xcconfig = {
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'DEFINES_MODULE' => 'YES',
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'VALID_ARCHS[sdk=iphonesimulator*]' => 'x86_64',
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'GCC_PREPROCESSOR_DEFINITIONS' => "FLUTTER_PACKAGE_PLUGIN_VERSION=\\@\\\"#{flutter_package_plugin_version}\\\""
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}
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s.resource_bundles = {'ably_flutter' => ['Resources/PrivacyInfo.xcprivacy']}
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s.swift_version = '5.0'
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s.test_spec 'Tests' do |ts|
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ts.source_files = 'Tests/**/*.{h,m}'
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ts.framework = 'XCTest'
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end
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end

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