Method shouldReloadWebView in CDVWebViewEngine misses condition, results in Blank Screen

[rcorin]

Bug Report

Problem

I'm investigating a situation when the app comes to foreground from background and the webview content process has been killed by the OS.
In shouldReloadWebView , CDVWebViewEngine.m:283, there is this code:

BOOL title_is_nil = (title == nil);
BOOL location_is_blank = [[location absoluteString] isEqualToString:@"about:blank"];

BOOL reload = (title_is_nil || location_is_blank);

however location is nil, hence is false and also title_is_nil is false, resulting in reload being false.

What is expected to happen?

If the location is nil, reload should be true, so the condition should be:

BOOL location_is_blank = location == nil || [[location absoluteString] isEqualToString:@"about:blank"];

What does actually happen?

the app gets stuck in a white screen because the reload isn't issued, due to shouldReloadWebView being false.

Information

To reproduce the issue, i had to actually run the app in simulator, kill the com.apple.WebKit.WebContent process with the app in background, and then comment out the other webview reloads until reaching the point of shouldReloadWebView.

Command or Code

See above info.

Environment, Platform, Device

iOS simulator

Version information

Xcode 14.3, iOS 12, Cordoba 10.0.0.

Checklist

• [X ] I searched for existing GitHub issues
• [ X] I updated all Cordova tooling to most recent version
• [ X] I included all the necessary information above

[BenLaKnet]

Hi,

I have the same issue. What should I do.

cordova-ios 7.1.1.

[horner]

Problem

It appears that when I background the Cordova app and use another application on iOS that uses lots of memory, when I return to the Cordova app it shows a white screen and appears to be frozen. There is no way to reload the page or navigate so I’m forced to kill the app and relaunch.

Captured the White Screen of Death in the debugger:

Here is a short: https://youtube.com/shorts/4rV0T_peIew?si=U60VhrfND7t9yftR

CDVWebViewEngine shouldReloadWebView::
CDVWebViewEngine shouldReloadWebView title: Stress-Energy Tensor Inquiry - Ozwell
CDVWebViewEngine shouldReloadWebView location: http://localhost:12992/session/sjrSNPmbYmHHkyAvb
CDVWebViewEngine shouldReloadWebView reload: 0
Clock discrepancy detected. Attempting re-sync.
Connection timeout. No sockjs heartbeat received.
HMR: websocket closed
HMR: connected
0x115002300 - GPUProcessProxy::didClose:
0x115002300 - GPUProcessProxy::gpuProcessExited: reason=Crash
0x115009230 - [PID=14401] WebProcessProxy::gpuProcessExited: reason=Crash
Error acquiring assertion: <Error Domain=RBSServiceErrorDomain Code=1 "((target is not running or doesn't have entitlement com.apple.developer.web-browser-engine.rendering AND target is not running or doesn't have entitlement com.apple.developer.web-browser-engine.networking AND target is not running or doesn't have entitlement com.apple.developer.web-browser-engine.webcontent))" UserInfo={NSLocalizedFailureReason=((target is not running or doesn't have entitlement com.apple.developer.web-browser-engine.rendering AND target is not running or doesn't have entitlement com.apple.developer.web-browser-engine.networking AND target is not running or doesn't have entitlement com.apple.developer.web-browser-engine.webcontent))}>
0x1150112b0 - ProcessAssertion::acquireSync Failed to acquire RBS assertion 'XPCConnectionTerminationWatchdog' for process with PID=14400, error: (null)
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d6be0 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d5680 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
0x11500ce30 - NetworkProcessProxy::didClose (Network Process 0 crash)
Error acquiring assertion: <Error Domain=RBSAssertionErrorDomain Code=2 "Specified target process 14402 does not exist" UserInfo={NSLocalizedFailureReason=Specified target process 14402 does not exist}>
0x115011550 - ProcessAssertion::acquireSync Failed to acquire RBS assertion 'XPCConnectionTerminationWatchdog' for process with PID=14402, error: (null)
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d4300 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d66a0 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
0x115009230 - [PID=14401] WebProcessProxy::didClose: (web process 0 crash)
0x115009230 - [PID=14401] WebProcessProxy::processDidTerminateOrFailedToLaunch: reason=Crash
Error acquiring assertion: <Error Domain=RBSAssertionErrorDomain Code=2 "Specified target process 14401 does not exist" UserInfo={NSLocalizedFailureReason=Specified target process 14401 does not exist}>
0x115011730 - ProcessAssertion::acquireSync Failed to acquire RBS assertion 'XPCConnectionTerminationWatchdog' for process with PID=14401, error: (null)
0x12add5518 - [pageProxyID=19, webPageID=20, PID=14401] WebPageProxy::processDidTerminate: (pid 14401), reason=Crash
0x12add5518 - [pageProxyID=19, webPageID=20, PID=14401] WebPageProxy::dispatchProcessDidTerminate: reason=Crash
Could not create a sandbox extension for '/var/containers/Bundle/Application/DBE77A25-7CC7-4636-90F7-1D5BC6558BFC/Ozwell.app'
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d7240 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d7a20 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
IAB.close() called but it was already closed.
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d5380 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d7a80 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
Failed to terminate process: Error Domain=com.apple.extensionKit.errorDomain Code=18 "(null)" UserInfo={NSUnderlyingError=0x12c5d7b10 {Error Domain=RBSRequestErrorDomain Code=3 "No such process found" UserInfo={NSLocalizedFailureReason=No such process found}}}
CDVWebViewEngine shouldReloadWebView::
CDVWebViewEngine shouldReloadWebView title:
CDVWebViewEngine shouldReloadWebView location: http://localhost:12992/session/sjrSNPmbYmHHkyAvb
CDVWebViewEngine shouldReloadWebView reload: 0
CDVWebViewEngine shouldReloadWebView::
CDVWebViewEngine shouldReloadWebView title:
CDVWebViewEngine shouldReloadWebView location: http://localhost:12992/session/sjrSNPmbYmHHkyAvb
CDVWebViewEngine shouldReloadWebView reload: 0
CDVWebViewEngine shouldReloadWebView::
CDVWebViewEngine shouldReloadWebView title:
CDVWebViewEngine shouldReloadWebView location: http://localhost:12992/session/sjrSNPmbYmHHkyAvb
CDVWebViewEngine shouldReloadWebView reload: 0
CDVWebViewEngine shouldReloadWebView::
CDVWebViewEngine shouldReloadWebView title:
CDVWebViewEngine shouldReloadWebView location: http://localhost:12992/session/sjrSNPmbYmHHkyAvb
CDVWebViewEngine shouldReloadWebView reload: 0
CDVWebViewEngine shouldReloadWebView::
CDVWebViewEngine shouldReloadWebView title:
CDVWebViewEngine shouldReloadWebView location: http://localhost:12992/session/sjrSNPmbYmHHkyAvb
CDVWebViewEngine shouldReloadWebView reload: 0
App is being debugged, do not track this hang
Hang detected: 1.17s (debugger attached, not reporting)
attempted to start async task 'Fetch Current User Activity' for RequestID(13003:5 = 55847459749893) but already 1036.96 ms past deadline
Handle connection with error: Connection interrupted

Here is the debugger:

Research on other people having the issue

There is an issue in meteor: meteor/meteor#11811 which mentions the cordova ticket #1235 which mentions a fix: https://github.com/apache/cordova-ios/pull/1533/files

by modifying CDVWebViewEngine.m:

NSURL* url = [((CDVViewController*) self.viewController) appUrl];
         NSURLRequest* appReq = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:20.0];
         [self loadRequest:appReq];

In the meteor ticket: banjerluke mentioned:
Unzip this folder and place it in cordova-build-override/platforms/ios in your project and Meteor will use the patched files when building the app:
https://github.com/user-attachments/files/20534411/CordovaLib.zip

The end result should be two files in these paths:

cordova-build-override/platforms/ios/CordovaLib/Classes/Private/Plugins/CDVWebViewEngine/CDVWebViewEngine.m
cordova-build-override/platforms/ios/CordovaLib/Classes/Public/CDVViewController.h

Our attempted fix

We tried the cordova-build-override/platforms/ios/CordovaLib/Classes/Private/Plugins/CDVWebViewEngine/CDVWebViewEngine.m file from https://github.com/user-attachments/files/20534411/CordovaLib.zip but that still did not fix it.

The actual fix

We need to detect in the CDVWebViewEngine.m when the GPUProcessProxy Crashes and reload the WebView. We fixed it in our code, but using the override and fixing it to reload when the title is null or empty. This has fixed the issue. We are making a PR to make sure this is fixed for everyone. I think this is an Apple bug, but Cordova is severely unstable for those that get into low memory conditions on their phone… Isn't that everyone?

We started PR here: #1552

[horner]

Moving comments that PR now

[dpogue]

I'd like to better understand if this impacts only Meteor apps, or Cordova projects as a whole. So far most of the comments seem to be mentioning Meteor, and I need to make sure that any changes we make on the Cordova side don't negatively impact non-Meteor apps.

[horner]

@dpogue This is an issue with Cordova. Rather it's an issue with iOS crashing out the safari process but leaving the app running. In my video https://youtube.com/shorts/4rV0T_peIew?si=U60VhrfND7t9yftR the WebGPU dies when a memory reclaim happens.

We just use meteor as a wrapper to cordova so that is why there is a lot of discussion about how to fix it there now too.

[dpogue]

The Cordova WKWebView implementation includes reload functionality when a process termination is detected (which should cover the GPU Process, the Network Process, and the Web Content Process):

cordova-ios/CordovaLib/Classes/Private/Plugins/CDVWebViewEngine/CDVWebViewEngine.m

Lines 563 to 566 in 41d8995

	- (void)webViewWebContentProcessDidTerminate:(WKWebView *)webView
	{
	[webView reload];
	}

Previous comments made it sound like the white screen was potentially due to bugs in how Meteor serves the web content, and so far nobody has provided an example where this is happening outside of a Meteor app.

[horner]

The problem is that the title is an empty string after the crash.

CDVWebViewEngine shouldReloadWebView title:
CDVWebViewEngine shouldReloadWebView location: http://localhost:12992/session/sjrSNPmbYmHHkyAvb
CDVWebViewEngine shouldReloadWebView reload: 0

[dpogue]

I tried to do some testing of this in the simulator with the default Cordova Hello World project, and I cannot reproduce the bug.

I tried:

1. Launching the app in the simulator, ensuring that it loaded.
2. Backgrounding and foregrounding the app and confirming that shouldReloadWebView had title and location set and returned false.
3. Backgrounding the app and killing the com.apple.WebKit.GPU process in Activity Monitor.
4. Foregrounding the app and confirming that shouldReloadWebView had title and location set and returned false and that webViewWebContentProcessDidTerminate was called to reload the webview.
5. Killing the com.apple.WebKit.WebContent process in Activity Monitor, and ensuring that webViewWebContentProcessDidTerminate was called immediately to reload the webview.

I can't be totally sure, but it seems to me like shouldReloadWebView might not even be necessary since webViewWebContentProcessDidTerminate seems to fire when expected to reload the webview content when a process crashes. I was never able to get into a state where shouldReloadWebView returned true.

Can this be reproduced in a non-Meteor app?

[erisu]

@horner Could you also check if there is any errors displayed in the Safari Web Inspector Console?

Errors could occur before you open Web Inspector and wont display in console as it might not be preserved. You might need to refresh the app by pressing ⌘ + r within the Web Inspector.

Just to make sure there are no errors here.

[horner]

@abroa01 please see comment above about safari console

Also take at look at #1355 (comment) and see if that function could be used instead of the reload function.

shouldReloadWebView might not even be necessary since webViewWebContentProcessDidTerminate

I still worry that shouldReloadWebView still needs fixing about the empty name or some other test of the crash of Safari unless it's made completely irrelevant by webViewWebContentProcessDidTerminate

I have one of my employees https://github.com/abroa01 looking into to it.

#1552 (comment)

[abroa01]

Update on our findings

We've been investigating this issue and have successfully implemented a workaround that's preventing the white screen problem in our app. I wanted to share our findings with the community.

What we discovered

Looking at the logs when the WebKit process crashes, we can confirm that webViewWebContentProcessDidTerminate IS being called in our case:

0x112009420 - [PID=15090] WebProcessProxy::didClose: (web process 0 crash)
0x113834e18 - [pageProxyID=19, webPageID=20, PID=15090] WebPageProxy::processDidTerminate: (pid 15090), reason=Crash
CDVWebViewEngine: Inside webViewWebContentProcessDidTerminate - Web content process terminated, reloading with cached URL
CDVWebViewEngine : Inside webViewWebContentProcessDidTerminate - using cached good URL for process termination reload: http://localhost:12280/?cdvToken=...

However, we also see that shouldReloadWebView is still being called periodically and returning 0 (false), confirming the original bug about the flawed nil checking logic:

CDVWebViewEngine shouldReloadWebView::
CDVWebViewEngine shouldReloadWebView title: Meteor App
CDVWebViewEngine shouldReloadWebView location: http://localhost:12280/register
CDVWebViewEngine shouldReloadWebView reload: 0

Our solution: Last good URL caching mechanism

We've implemented a URL caching approach that stores successful page loads and uses them during recovery scenarios. Here are the key changes to CDVWebViewEngine.m:

1. Cache successful navigations

- (void)webView:(WKWebView*)webView didFinishNavigation:(WKNavigation*)navigation
{
    // Always cache successful URL loads
    if (webView.URL && ![webView.URL.absoluteString isEqualToString:@"about:blank"] && ![webView.URL.absoluteString isEqualToString:@""]) {
        self.lastGoodURL = webView.URL;
        NSLog(@"CDVWebViewEngine cached good URL: %@", webView.URL.absoluteString);
    }
    
    [[NSNotificationCenter defaultCenter] postNotification:[NSNotification notificationWithName:CDVPageDidLoadNotification object:webView]];
}

2. Enhanced recovery in webViewWebContentProcessDidTerminate

- (void)webViewWebContentProcessDidTerminate:(WKWebView *)webView
{
    NSLog(@"CDVWebViewEngine: Inside webViewWebContentProcessDidTerminate - Web content process terminated, reloading with cached URL");
    
    NSURL* currentURL = webView.URL;
    NSURL* url;
    
    if (self.lastGoodURL) {
        url = self.lastGoodURL;  // Priority 1: Last known good URL
        NSLog(@"CDVWebViewEngine : Inside webViewWebContentProcessDidTerminate - using cached good URL for process termination reload: %@", url.absoluteString);
    } else if (currentURL && ![currentURL.absoluteString isEqualToString:@"about:blank"] && ![currentURL.absoluteString isEqualToString:@""]) {
        url = currentURL;  // Priority 2: Current URL
        NSLog(@"CDVWebViewEngine : Inside webViewWebContentProcessDidTerminate - using current page URL for process termination reload: %@", url.absoluteString);
    } else {
        url = [((CDVViewController*) self.viewController) appUrl];  // Priority 3: App URL
        NSLog(@"CDVWebViewEngine : Inside webViewWebContentProcessDidTerminate - using fallback app URL for process termination reload: %@", url.absoluteString);
    }
    
    NSURLRequest* appReq = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:20.0];
    [webView loadRequest:appReq];
}

3. Same approach for onAppWillEnterForeground

- (void) onAppWillEnterForeground:(NSNotification*)notification {
    if ([self shouldReloadWebView]) {
        NSLog(@"%@", @"CDVWebViewEngine reloading!");
        
        WKWebView* wkWebView = (WKWebView*)_engineWebView;
        NSURL* currentURL = wkWebView.URL;
        
        NSURL* url;
        if (self.lastGoodURL) {
            url = self.lastGoodURL;
            NSLog(@"CDVWebViewEngine using cached good URL for reload: %@", url.absoluteString);
        } else if (currentURL && ![currentURL.absoluteString isEqualToString:@"about:blank"] && ![currentURL.absoluteString isEqualToString:@""]) {
            url = currentURL;
            NSLog(@"CDVWebViewEngine using current page URL for reload: %@", url.absoluteString);
        } else {
            url = [((CDVViewController*) self.viewController) appUrl];
            NSLog(@"CDVWebViewEngine using fallback app URL for reload: %@", url.absoluteString);
        }
        
        NSURLRequest* appReq = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:20.0];
        [wkWebView loadRequest:appReq];
    }
}

4. Additional safety in shouldReloadWebView

- (BOOL)shouldReloadWebView:(NSURL*)location title:(NSString*)title
{
    BOOL title_is_nil = (title == nil) || [title isEqualToString:@""];
    BOOL location_is_blank = [[location absoluteString] isEqualToString:@"about:blank"];
    
    BOOL reload = (title_is_nil || location_is_blank);
    
    // Debug logs showing the evaluation
    NSLog(@"CDVWebViewEngine shouldReloadWebView::");
    NSLog(@"CDVWebViewEngine shouldReloadWebView title: %@", title);
    NSLog(@"CDVWebViewEngine shouldReloadWebView location: %@", [location absoluteString]);
    NSLog(@"CDVWebViewEngine shouldReloadWebView reload: %u", reload);
    
    return reload;
}

What the logs prove

From our test session logs:

1. WebKit process crashes: WebProcessProxy::didClose: (web process 0 crash)
2. Our handler fires immediately: CDVWebViewEngine: Inside webViewWebContentProcessDidTerminate
3. Successfully recovers using cached URL: using cached good URL for process termination reload: http://localhost:12280/?cdvToken=...
4. App reloads without white screen ✓

This recovery mechanism triggered multiple times during our testing (you can see multiple crash/recovery cycles in the logs), and the app successfully recovered each time.

Results

With these changes, our app now successfully recovers from WebKit process terminations without showing the white screen. The app reloads to the last known good state instead of getting stuck.

[dpogue]

The concern with checking for an empty title is that it's completely valid for a page to have no <title> tag, or an empty <title></title> tag, and the proposed fix would result in that page constantly reloading. That would be an unexpected, web-incompatible, and breaking change for existing Cordova apps.

From what I saw in my testing, shouldReloadWebView should be completely irrelevant with webViewWebContentProcessDidTerminate working properly.

[dpogue]

Looking at history, it looks like originally webViewWebContentProcessDidTerminate wasn't always called reliably by the system, which led to implementing shouldReloadWebView: https://issues.apache.org/jira/browse/CB-9888

The original shouldReloadWebView implementation did check for a blank title: apache/cordova-plugin-wkwebview-engine@815ed07

And it was determined to be too aggressive and causing issues for apps: https://issues.apache.org/jira/browse/CB-11554
apache/cordova-plugin-wkwebview-engine@6d39ff1

So reloading on a non-null but empty title is definitely a bug that we do not want to re-introduce.