iOS WKWebView JavaScriptCore WTFCrash

Question

I added an webview instance on our app. But, sometimes crash occurs. The crash called JavaScriptCore WTFCrash on call stack.

Crashed: com.apple.main-thread
0  JavaScriptCore                 0x26062a22 WTFCrash + 53
1  JavaScriptCore                 0x260629cd WTFPrintBacktrace + 128
2  WebKit                         0x29a2ab95 WTF::HashTable<unsigned long long, WTF::KeyValuePair<unsigned long long, WTF::RefPtr<WebKit::CallbackBase> >, WTF::KeyValuePairKeyExtractor<WTF::KeyValuePair<unsigned long long, WTF::RefPtr<WebKit::CallbackBase> > >, WTF::IntHash<unsigned long long>, WTF::HashMap<unsigned long long, WTF::RefPtr<WebKit::CallbackBase>, WTF::IntHash<unsigned long long>, WTF::HashTraits<unsigned long long>, WTF::HashTraits<WTF::RefPtr<WebKit::CallbackBase> > >::KeyValuePairTraits, WTF::HashTraits<unsigned long long> >::begin() const + 30
3  WebKit                         0x29a2ab4d WTF::Vector<WTF::RefPtr<WebKit::CallbackBase>, 0ul, WTF::CrashOnOverflow, 16ul>::reserveCapacity(unsigned long) + 24
4  WebKit                         0x29a2aaa5 WTF::Vector<WTF::RefPtr<WebKit::CallbackBase>, 0ul, WTF::CrashOnOverflow, 16ul>::resize(unsigned long) + 44
5  WebKit                         0x29a2a955 void WebKit::invalidateCallbackMap<WTF::RefPtr<WebKit::CallbackBase> >(WTF::HashMap<unsigned long long, WTF::RefPtr<WebKit::CallbackBase>, WTF::IntHash<unsigned long long>, WTF::HashTraits<unsigned long long>, WTF::HashTraits<WTF::RefPtr<WebKit::CallbackBase> > >&, WebKit::CallbackBase::Error) + 104
6  WebKit                         0x29ad18b1 WebKit::WebPageProxy::resetState(WebKit::WebPageProxy::ResetStateReason) + 456
7  WebKit                         0x29ad0897 WebKit::WebPageProxy::close() + 78
8  WebKit                         0x29b8496d -[WKWebView dealloc] + 120
9  libobjc.A.dylib                0x223c13a9 (anonymous namespace)::AutoreleasePoolPage::pop(void*) + 388
10 CoreFoundation                 0x22b1af89 _CFAutoreleasePoolPop + 16
11 CoreFoundation                 0x22b2a251 -[__NSArrayI enumerateObjectsWithOptions:usingBlock:] + 140
12 UIKit                          0x2719f2ed -[UIViewController _setViewAppearState:isAnimating:] + 1088
13 UIKit                          0x272152d1 -[UIViewController __viewDidDisappear:] + 172
14 UIKit                          0x2719f6d3 -[UIViewController _endAppearanceTransition:] + 258
15 UIKit                          0x2725b6fb -[UINavigationController navigationTransitionView:didEndTransition:fromView:toView:] + 886
16 UIKit                          0x2733680f __49-[UINavigationController _startCustomTransition:]_block_invoke + 210
17 UIKit                          0x272b4157 -[_UIViewControllerTransitionContext completeTransition:] + 90
18 UIKit                          0x27418c7b __53-[_UINavigationParallaxTransition animateTransition:]_block_invoke95 + 682
19 UIKit                          0x271c1ba5 -[UIViewAnimationBlockDelegate _didEndBlockAnimation:finished:context:] + 540
20 UIKit                          0x271c1685 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] + 204
21 UIKit                          0x271c157f -[UIViewAnimationState animationDidStop:finished:] + 78
22 QuartzCore                     0x25221689 CA::Layer::run_animation_callbacks(void*) + 252
23 libdispatch.dylib              0x2277980f _dispatch_client_callout + 22
24 libdispatch.dylib              0x22787ba9 _dispatch_main_queue_callback_4CF$VARIANT$mp + 1524
25 CoreFoundation                 0x22bcdb6d __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
26 CoreFoundation                 0x22bcc067 __CFRunLoopRun + 1574
27 CoreFoundation                 0x22b1b229 CFRunLoopRunSpecific + 520
28 CoreFoundation                 0x22b1b015 CFRunLoopRunInMode + 108
29 GraphicsServices               0x2410bac9 GSEventRunModal + 160
30 UIKit                          0x271ef189 UIApplicationMain + 144
31 App                            0x12d600 main (AppDelegate.swift:14)
32 libdispatch.dylib              0x227c3873 (Missing)

Does anybody has experienced similar this issue?

Answer 1

Your code has two issues: - stringByEvaluatingJavaScriptFromString: returns an autoreleased NSString. You thus do not need to use stringWithFormat:. - Your code does not have a valid format either.

pageText = [NSString stringWithFormat:@"%@", [webView stringByEvaluatingJavaScriptFromString:@"document.body.innerHTML"];

would correct the format error, however, because you are assigning pageText you run the risk of a crash later due to the autorelease.

The following is all that is necessary. NB: I am assuming that the Javascript is valid....

- (void)webViewDidFinishLoad:(UIWebView *)webView {
    [pageText release], pageText = nil;

    pageText = [[webView stringByEvaluatingJavaScriptFromString:@"document.body.innerHTML"] retain];

    if (!pageText)
        // innerHTML was empty
        pageText = [[webView stringByEvaluatingJavaScriptFromString:@"document.body"] retain];
}

Note that the retain is added because you are assigning the pageText ivar instead of using a setter. Make sure you add [pageText release]; in your dealloc to prevent leaks. Be very careful when trying to access pageText elsewhere in your code as it could still be nil. Be defensive.