Firebase Crashlytics MacOS - all crashes under AppKit - ios

Question

I have an iOS app that is ported to MacOS. The app uses Firebase for Crashlytics. So far I managed to configure everything just fine, by creating a separate Mac target and separate Firebase project for that target. The problem is that the crashes I see in the console for the MacOS project are all under "AppKit". Example:
AppKit | -[NSApplication _crashOnException:] + 106
Not very informative, is it... Now, I can still get the crashing exception if I inspect the crashes and then go to 'Keys':
crash_info_entry_0 | Crashing on exception: *** -[__NSCFCalendar rangeOfUnit:startDate:interval:forDate:]: date cannot be nil
But with that all the different crashes are grouped together under that AppKit crash and so it is not very helpful.
I realise that this issue is due to the default behaviour of AppKit catching all exceptions on MacOS by default. Is there perhaps a better way to setup Crashlytics for MacOS, in order to get more granular reports, like on iOS and other platforms?

Answer 1

After a lot of research I found that there is no perfect solution to this. I tried overriding NSApplication and setting it as NSPrincipalClass, and even implemented Sentry instead - no success. But I found a way to bypass AppKit using method swizzling and FIRExceptionModel.
Note: Before anything, for Firebase Crashlytics to work on MacOS, you need the following in your AppDelegate's didFinishLaunchingWithOptions:
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
[userDefaults registerDefaults:#{#"NSApplicationCrashOnExceptions" : #"YES"}];
Then you need to create a category of NSApplication and swizzle the method _crashOnException:
#import <objc/runtime.h>
#import "NSApplication+CrashReport.h"
#import <FIRCrashlytics.h>
#implementation NSApplication (CrashReport)
+(void)load {
static dispatch_once_t once_token;
dispatch_once(&once_token, ^{
SEL crashOnExceptionSelector = #selector(_crashOnException:); // Ignore 'Undeclared selector' warning.
SEL crashOnExceptionReporterSelector = #selector(reported__crashOnException:);
Method originalMethod = class_getInstanceMethod(self, crashOnExceptionSelector);
Method extendedMethod = class_getInstanceMethod(self, crashOnExceptionReporterSelector);
method_exchangeImplementations(originalMethod, extendedMethod);
});
}
- (void)reported__crashOnException:(NSException*)exception {
NSArray<NSString*> *stacktrace = [exception callStackSymbols];
[[FIRCrashlytics crashlytics]setCustomValue:stacktrace forKey:#"mac_os_stacktrace"];
FIRExceptionModel *errorModel = [FIRExceptionModel exceptionModelWithName:exception.name reason:exception.reason];
// The below stacktrace is hardcoded as an example, in an actual solution you should parse the stacktrace array entries.
errorModel.stackTrace = #[
[FIRStackFrame stackFrameWithSymbol:#"This stacktrace is fabricated as a proof of concept" file:#"Hello from Serge" line:2021],
[FIRStackFrame stackFrameWithSymbol:#"__exceptionPreprocess" file:#"CoreFoundation" line:250],
[FIRStackFrame stackFrameWithSymbol:#"objc_exception_throw" file:#"libobjc.A.dylib" line:48],
[FIRStackFrame stackFrameWithSymbol:#"-[__NSCFCalendar rangeOfUnit:startDate:interval:forDate:]" file:#"CoreFoundation" line:453]
];
// Note: ExceptionModel will always be reported as a non-fatal.
[[FIRCrashlytics crashlytics] recordExceptionModel:errorModel];
[self reported__crashOnException:exception];
}
#end
This code as a gist: https://gist.github.com/sc941737/c0c4542401ce203142c93ddc9b05eb1f
This means however that the exceptions won't be reported as crashes, but as non-fatals. So I would recommend setting an extra custom key to filter crashes from non-fatals more easily. See Firebase docs for details: https://firebase.google.com/docs/crashlytics/customize-crash-reports?platform=ios
NOTE: Swizzling private methods of Apple's APIs is a no-no for apps targeting the app store. It wasn't an issue in my case, because it was an app used internally.