Swift app crash with mutateError on NSMutableString object

Question

AnST OP

Created Feb ’24

Replies 1

Boosts 0

Participants 2

Here's my codes:

extension NSMutableString {
    
    func clear() {
        replaceCharacters(in: NSRange(location: 0, length: length), with: String(data: Data.init(repeating: 0, count: length), encoding: .utf8)!)
        replaceCharacters(in: NSRange(location: 0, length: length), with: "")
    }
    
}

My app receive some random rare crash report on the line: replaceCharacters(in: NSRange(location: 0, length: length), with: String(data: Data.init(repeating: 0, count: length), encoding: .utf8)!)

Crash logs:

Last Exception Backtrace:
0   CoreFoundation                	0x19f228870 __exceptionPreprocess + 164 (NSException.m:249)
1   libobjc.A.dylib               	0x197543c00 objc_exception_throw + 60 (objc-exception.mm:356)
2   CoreFoundation                	0x19f2f0d10 _CFThrowFormattedException + 108 (CFObject.m:2245)
3   CoreFoundation                	0x19f26094c mutateError + 96 (CFObject.m:599)
4   CoreFoundation                	0x19f185770 -[__NSCFString replaceCharactersInRange:withString:] + 72 (CFObject.m:608)
5   MyApp                    	0x10122c67c NSMutableString.clear() + 224 (NSMutableString.swift:22)
6   MyApp                    	0x1012974f4 UserData.loggedOut() + 56 (UserData.swift:58)
7   MyApp                    	0x100fac7dc AuthenticationManager.didLogout(isSessionExpired:preventAutoLoginByFaceID:) + 60 (AuthenticationManager.swift:200)

The thing is I couldn't reproduce it and the crash is rare so I run out of idea, and would hope to receive some suggestions from the forum. Thank you.

Boost

Answer 1

DTS Engineer OP

Apple

Feb ’24

Internally, -replaceCharactersInRange:withString: calls through to a CF-level function, __CFStringCheckAndReplace. If that fails, it calls this mutateError routine which throws an exception. AFAIK that part is not open source, but the __CFStringCheckAndReplace is. You can find it in the Swift Foundation source code here. That should give you some idea as to the potential causes for this failure.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

0