[deep link][ios] Update openURL method to reflect the result from framework #52643

hangyujin · 2024-05-07T23:18:50Z

follow up on comments on #52350

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hangyujin · 2024-05-08T23:51:35Z

i realized
openURL:options:completionHandler: is an async method
but application:openURL:options:(https://developer.apple.com/documentation/uikit/uiapplicationdelegate/1623112-application?language=objc ) is a non-async method so I cannot just add a completionHandler to it ,

So i guess the return value of it can only reflect the deep link flag value, not the bool result from framework then.

chunhtai · 2024-05-09T20:20:29Z

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

+- (void)openURL:(NSURL*)url
+              options:(NSDictionary<UIApplicationOpenExternalURLOptionsKey, id>*)options
+    completionHandler:(void (^)(BOOL success))completion {
+  if (![self isFlutterDeepLinkingEnabled]) {


Even this is No, we still want to go through plugins, I think?

Can you explain why we want to do that?

for those who use uni-link or their own plugin to handle deeplink, they would set this to no, right?

Yes they would set this to no.
but for those using uni-link and didn't set isFlutterDeepLinkingEnabled flag, the current behavior is already return NO for these methods and don't invoke the framework method. This PR is not changing their experience.

you are right, I misread the code, looks like the plugin would have been called already before reaching here.

chunhtai · 2024-05-09T20:21:33Z

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

@@ -171,7 +188,14 @@ - (BOOL)application:(UIApplication*)application
  if ([_lifeCycleDelegate application:application openURL:url options:options]) {
    return YES;
  }
-  return [self openURL:url];
+  if (![self isFlutterDeepLinkingEnabled]) {


do we still ned this check if we go delegate to other selector in line 194?

I just add this so the return value reflect the value of the flag.

chunhtai · 2024-05-09T20:23:22Z

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

+                options:options
+      completionHandler:^(BOOL success){
+      }];
+  return YES;


can this method get the result from completion handler only?

Also is implementing this selector optional if we already implement the one with completionhandler?

can this method get the result from completion handler only?>>

this application:openURL:options: method is non-async, i don't think its return value can be set from the completion handler so i used the deep link flag value.

But should this method return before the completion handler is complete? Before, this method didn't return until pushRouteInformation was actually sent, whereas now it would return instantly.
It seems like you'd want to spin the runloop until the completion handler was done, and then return the value from the completion handler.

what's the best practice to "spin the runloop"?

I updated the code to wait for the completion handler but got failures :

Failures for clang-tidy on /Volumes/Work/s/w/ir/cache/builder/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterAppDelegate.mm:
/Volumes/Work/s/w/ir/cache/builder/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterAppDelegate.mm:178:3: error: Waiting on a callback using a semaphore creates useless threads and is subject to priority inversion; consider using a synchronous API or changing the caller to be asynchronous [clang-analyzer-optin.performance.GCDAntipattern,-warnings-as-errors]
178 | dispatch_semaphore_wait(semaphore, 5 * NSEC_PER_SEC);

chunhtai

LGTM

chunhtai · 2024-05-13T16:19:47Z

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

+- (void)openURL:(NSURL*)url
+              options:(NSDictionary<UIApplicationOpenExternalURLOptionsKey, id>*)options
+    completionHandler:(void (^)(BOOL success))completion {
+  if (![self isFlutterDeepLinkingEnabled]) {


you are right, I misread the code, looks like the plugin would have been called already before reaching here.

jmagman · 2024-05-13T20:46:23Z

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

@@ -149,18 +155,29 @@ - (BOOL)openURL:(NSURL*)url {
                     if (didTimeout) {


Now that this is async, can we get rid of the waitForFirstFrame?

I remembered this was added to workaround the issue that when we receive openurl, we don't know what the current state of flutter is in. If we send if before the first frame is drawn, the message will be dropped because the widgetbindingobserver is not yet registered. It is also too late to set initialroute at this point since it is already consumed by the framework.

but this was a long time ago, I am not sure if this is still the case

It seems like FlutterAppDelegate needs to know a lot of details about the engine, the navigationChannel, and the available method. What if this changed to:

- (void)openURL:(NSURL*)url options:(NSDictionary<UIApplicationOpenExternalURLOptionsKey, id>*)options completionHandler:(void (^)(BOOL success))completion { if (![self isFlutterDeepLinkingEnabled]) { completion(NO); } else { FlutterViewController* flutterViewController = [self rootFlutterViewController]; if (flutterViewController) { [flutterViewController openDeepLink:url completionHandler:completion]; } else { FML_LOG(ERROR) << "Attempting to open an URL without a Flutter RootViewController."; completion(NO); } } }

FlutterViewController_Internal.h

- (void)openDeepLink:(NSURL*)url completionHandler:(void (^)(BOOL success))completion;

and then in FlutterViewController:

- (void)openDeepLink:(NSURL*)url completionHandler:(void (^)(BOOL success))completion { [_engine.get() waitForFirstFrame:3.0 callback:^(BOOL didTimeout) { if (didTimeout) { FML_LOG(ERROR) << "Timeout waiting for the first frame when launching an URL."; completion(NO); } else { // invove the method and get the result [[_engine.get() navigationChannel] invokeMethod:@"pushRouteInformation" arguments:@{ @"location" : url.absoluteString ?: [NSNull null], } result:^(id _Nullable result) { BOOL success = [result isKindOfClass:[NSNumber class]] && [result boolValue]; if (!success) { // Logging the error if the result is not successful FML_LOG(ERROR) << "Failed to handle route information in Flutter."; } completion(success); }]; } }]; }

yup, It does seem like the viewcontroller may be a better place to put these logic

thanks, this looks good, updated!

jmagman · 2024-05-14T20:35:24Z

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

+  // Use a dispatch semaphore to wait for the completion handler
+  dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);


You won't want a dispatch_semaphore on the main thread, that will cause hangs and potentially deadlocks.

The run loop is a processing loop for event handling, and there's one assigned to the main thread. I believe what you want is to kick off the request, and spin the main run loop until it completes, then return the value from this method.

I didn't run this code so you should test it, but something like:

__block BOOL openURLSuccess = NO; __block BOOL openURLCompleted = NO; [self openURL:url options:options completionHandler:^(BOOL success) { openURLSuccess = success; openURLCompleted = YES; }]; while (!openURLCompleted) { [NSRunLoop.currentRunLoop runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1]]; } return openURLSuccess;

Thanks for educating me about the The run loop

I have some more questions :

is a while loop a form of busy waiting and will it cause some performance issues? Should i also add a timeout to prevent an infinite loop?

Looks like the async api [openURL:options:completionHandler:] is newer than the non-async api [application:openURL:options:] , is it possible the async one is replacing the non-async one? if so, it may be ok the async api returns the value from the framework but the old non-async api remains the old behavior to return the flag value.

is a while loop a form of busy waiting and will it cause some performance issues? Should i also add a timeout to prevent an infinite loop?

Are you concerned the code you're calling didTimeout logic won't work? You could pass in that timeout into the view controller method so it's obvious it handles timing out?

I'm also a bit concerned " navigationChannel invokeMethod:arguments:result: " will time out 😅 Is it possible?

You could add a timeout instead of the while loop, that would work too. And return NO if it times out.
There are a lot of timeouts going on here, it seems like it would be bad if it times out but the pushRouteInformation request has gone through, but not yet returned?

basically it's like

- (void)fakedispatch:(void (^)(BOOL success))completion { dispatch_queue_t queue = dispatch_get_main_queue(); dispatch_async(queue, ^{ NSLog(@"fakedispatch:completionHandler: "); completion(YES); }); } - (void)fakeRunloop { __block BOOL completed = NO; CFTimeInterval startTime = CACurrentMediaTime(); [self fakedispatch:^(BOOL success) { completed = YES; }]; while (!completed) { NSLog(@"runing loop %f", CACurrentMediaTime() - startTime); [NSRunLoop.currentRunLoop runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1.0]]; } }

and it will be a deadlock

@hangyujin I just tried the above code in a dummy project and didn't get a deadlock. Note that im calling from viewDidLoad, but the idea should be similar.

@implementation ViewController - (void)viewDidLoad { [super viewDidLoad]; [self fakeRunloop]; NSLog(@"completed fakeRunLoop"); } @end

As you can see NSLog(@"completed fakeRunLoop"); gets printed out.

What exact behavior are you observing? Does it hang?

I called it from application:continueUserActivity:restorationHandler because this method will be invoked by deep linking,

- (BOOL)application:(UIApplication*)application continueUserActivity:(NSUserActivity*)userActivity restorationHandler: (void (^)(NSArray<id<UIUserActivityRestoring>>* __nullable restorableObjects)) restorationHandler { NSLog(@"application:continueUserActivity:restorationHandler"); [self fakeRunloop]; NSLog(@"completed fakeRunLoop"); return NO; }

And it's just running forever and can't complete

I will look into this today

Just wanna update my progress so far. So for the deadlock, I wasn't able to find anything useful online, but I did come up with a theory - the continueUserActivity runs on main queue (hence also the main thread); the viewDidLoad runs on main thread, but NOT the main queue. This can explain why it works in viewDidLoad, but deadlock in continueUserActivity.

If my theory is correct, I don't think there's a way to synchronize the async API. I am thinking about a workaround (which I am still hashing out). Basically we want to return YES synchronously (marking as "handled"), then call the async API. If the async API comes back as failure, then call UIAppilcation::openURL which should throw the url back to iOS. Something like:

- (BOOL) continueUserActivity { if vc not present { return NO; } runAsyncAPI(completion: (success) { if (!success) { // throw it back to iOS [UIApplication.sharedApplication openURL: url] } }) return YES; }

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

hangyujin · 2024-05-16T20:14:46Z

@jmagman ping for review

hellohuanlin · 2024-05-16T22:56:38Z

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

-    // Not set or NO.
-    return NO;
+  // if not set, return NO
+  return isDeepLinkingEnabled ? [isDeepLinkingEnabled boolValue] : NO;


nit: this can be just isDeepLinkingEnabled.boolValue since sending message to nil will return NO.

I will keep this and flip NO to YES in #52350

hellohuanlin · 2024-05-16T23:00:26Z

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

+  while (!openURLCompleted) {
+    [NSRunLoop.currentRunLoop runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1]];
+  }
+  return openURLSuccess;


nit: can you write a helper to avoid duplicate code?

hellohuanlin · 2024-05-16T23:06:09Z

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

+
+  while (!openURLCompleted) {
+    [NSRunLoop.currentRunLoop runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1]];
+  }


Optional: If you are iffy about using BOOL flag for completeness, a semaphore version can be (pseudocode):

__block BOOL openURLSuccess = NO; dispatch_semaphore_t semaphore = dispatch_semaphore_create(0); [self openURL: url ... { openURLSuccess = success; dispatch_semaphore_signal(semaphore) }]; while (dispatch_semaphore_wait(semaphore, DISPATCH_TIME_NOW)) { [NSRunLoop.currentRunLoop runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1]]; }

Though a BOOL flag would be equally as good, since callback happens on main thread. I don't have a preference here.

Oh I just saw @jmagman's comment on semaphore.

To use semaphore on the same thread, you can't block it due to deadlock, as jenn previously commented. Instead, you pass in DISPATCH_TIME_NOW in dispatch_semaphore_wait, and then kick off the runloop so it can pick up the completion handler.

zanderso · 2024-05-30T20:14:18Z

From PR triage: What is the status of this PR? @hangyujin is this ready for another review pass from @hellohuanlin?

hellohuanlin · 2024-05-30T22:59:31Z

From PR triage: What is the status of this PR? @hangyujin is this ready for another review pass from @hellohuanlin?

There's a deadlock issue that I am looking into and will unblock @hangyujin when it's done.

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Set deep linking flag to true by default #52350

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hangyujin changed the title ~~[ios] Update openURL method to reflect the result from framework~~ [deep link][ios] Update openURL method to reflect the result from framework May 23, 2024

		@@ -149,18 +155,29 @@ - (BOOL)openURL:(NSURL*)url {
		if (didTimeout) {

		// Use a dispatch semaphore to wait for the completion handler
		dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);

[deep link][ios] Update openURL method to reflect the result from framework #52643

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[deep link][ios] Update openURL method to reflect the result from framework #52643

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hangyujin commented May 7, 2024 • edited

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