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How to access hidden iOS APIs and enhance
development efficacy.
2024/08/23 10:50ʙ
Track B
Regular talkʢ20 minʣ
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noppe
• Indie app developer
• DAWN for mastodon
• vear - VTuber camera
app
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DeNA Co., Ltd.,
• 2016 ~
• Pococha
• iOS Senior App Developer
• Code de Crossword at DeNA
booth
• They are sponsoring my talk
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Enjoy my talk!
• The talk will be in Japanese
• Slides are in English
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Agenda
• Perform
• Usecase
• Find
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Agenda
• Perform
• Usecase
• Find
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ObjC Private API
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ObjC Private API
Sample *object = [Sample new];
// Success
[object send];
// Error
[object validate];
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ObjC Private API
You can expose the method by adding a header file yourself.
@interface Sample (Private)
- (BOOL)validate;
@end
// Success
[objcect validate];
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ObjC Private API
You can call the method by using performSelector without adding a header file.
[object performSelector:NSSelectorFromString(@"validate")];
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ObjC Private API
object.isValidate = YES;
object.performSelector(
NSSelectorFromString(@"setIsValidate:"),
withObject: @(YES)
);
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Swift Hidden API
• Swift does not have any header file.
• Dynamic Link Framework has Swift module data.
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Swift Hidden API
• tbd file
• dynamic library stub for Eager linking 4
• public and internal api list
• swiftinterface file
• public api list
4 https://developer.apple.com/jp/videos/play/wwdc2022/110364/
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Swift Hidden API
/Applications
/Xcode.app
/Contents
/Developer
/Platforms
/iPhoneSimulator.platform
/Developer
/SDKs
/iPhoneSimulator.sdk
/System
/Library
/Frameworks
/SwiftUI.framework
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Swift Hidden API
SwiftUI.framework
├── Headers
│ ├── SwiftUI.h
│ └── SwiftUI_Metal.h
├── Modules
│ ├── SwiftUI.swiftmodule
│ │ ├── arm64-apple-ios-simulator.swiftdoc
│ │ ├── arm64-apple-ios-simulator.swiftinterface
│ │ ├── x86_64-apple-ios-simulator.swiftdoc
│ │ └── x86_64-apple-ios-simulator.swiftinterface
│ └── module.modulemap
└── SwiftUI.tbd
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Swift Hidden API
arm64-apple-ios-simulator.swiftinterface
...
@_Concurrency.MainActor
open class UIHostingController : UIKit.UIViewController
where Content : SwiftUICore.View {
@_Concurrency.MainActor @preconcurrency
public var _disableSafeArea: Swift.Bool {
get
set
}
}
...
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Swift Hidden API
let vc = UIHostingController(rootView: ContentView())
vc._disableSafeArea = true
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Swift Hidden API
SwiftUI.tbd
--- !tapi-tbd
tbd-version: 0
targets: [ i386-ios-simulator, x86_64-ios-simulator, arm64-ios-simulator ]
install-name: '/System/Library/Frameworks/SwiftUI.framework/SwiftUI'
current-version: 0.0.0
swift-abi-version: 0
exports:
- targets: [ i386-ios-simulator, x86_64-ios-simulator, arm64-ios-simulator ]
symbols: [ ... ]
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Swift Hidden API
SwiftUI.tbd (exports/symbols)
...
'_$s7SwiftUI4ViewPAAE12userActivity...',
'_$s7SwiftUI4ViewPAAE12userActivity...',
'_$s7SwiftUI4ViewPAAE12userActivity...',
'_$s7SwiftUI4ViewPAAE12userActivity...',
'_$s7SwiftUI4ViewPAAE12variableBlur...',
'_$s7SwiftUI4ViewPAAE12variableBlur...',
...
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Swift Hidden API
swift demangle '_$s7SwiftUI4....'
_$s7SwiftUI4.... --->
View.variableBlur(maxRadius: CGFloat, mask: Image, opaque: Bool) -> some
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Swift Hidden API
modify swiftinterface file yourself
@available(iOS 17.0, macOS 14.0, watchOS 10.0, tvOS 17.0, *)
extension SwiftUICore.View {
nonisolated public func variableBlur(
maxRadius: CoreFoundation.CGFloat,
mask: SwiftUI.Image,
opaque: Swift.Bool
) -> some SwiftUI.View
}
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Swift Hidden API
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UnderscoredAttributes1 5
extension View {
@_disfavoredOverload
func badge(_ count: Int) -> some View {
// ...
}
}
5 https://github.com/swiftlang/swift/pull/37854
1 https://github.com/swiftlang/swift/blob/main/docs/ReferenceGuides/UnderscoredAttributes.md
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Agenda
• Perform
• Usecase
• Find
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Hidden API's risk
⚠
• Semantics are subject to change.
• Side-effects are not controllable.
• AppStore rejection
• Uncompliance in review guildeline 2.5.12
2 https://developer.apple.com/jp/app-store/review/guidelines/
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Lowering risk
• Testing for lowing changing and side-effects risk.
func testPrivateMethod() {
let object = Sample()
let selector = #Selector("setUserName:")
object.performSelector(selector, withObject: "noppe")
#expect(object.userName == "noppe")
if !object.responds(selector) {
fatalError("Selector not found")
}
}
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Lowing risk
• Use beta for early detection
changes.
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What's the best usecase?
Development Phase Suitable
Concept Development !
Testing ⾠
Product Development "
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Concept Development
• Concept Development, Hackathon, UI Design, and more.
• Troublesome implementation
• Difficult implementation
• Complex visual effect
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UITextView.setAttributedPlaceholder:8
extension UITextView {
func setPlaceholder(_ placeholder: String?) {
let string = placeholder.map(NSAttributedString.init)
let selector = Selector(("setAttributedPlaceholder:"))
if responds(to: selector) {
perform(selector, with: string)
}
}
}
8 https://gist.github.com/AdamWhitcroft/c6ffc0323b9ce227588df7145685ae26#file-wrappeduitextview-swift-L41
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UINavigationItem._setWeeTitle:7
extension UINavigationItem {
func setWeeTitle(_ title: String) {
let selector = Selector(("_setWeeTitle:"))
if responds(to: selector) {
perform(selector, with: title as NSString)
}
}
}
7 https://github.com/feedback-assistant/reports/issues/506
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UINavigationItem._setWeeTitle:
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_UIHostingView
let view = _UIHostingView(rootView: ContentView())
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Testing
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Testing
UIDebuggingInformationOverla
y
• iOS10
• easy to use
• iOS11+
• needs to jump through
some hoops
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Instruments
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Product Development
Using hidden API is risky.
But, You can learn API design from hidden APIs.
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API naming
You can learn API naming rules from official SDK headers.
-(void)_endScrollingCursorOverrideIfNecessary;
-(UIOffset)_firstPageOffset;
-(id)_frameLayoutGuideIfExists;
(note) Don't override the method names, because ObjC uses Dynamic Dispatch.
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API design
You can learn UI scructures and architectures.
@interface UITextView : UIScrollView {
_UITextContainerView* _containerView;
...
}
...
@end
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How to find hidden APIs?
• Read swiftinterface, tbd and headers.
• Get method name list
• Read the stacktrace
• Find SNS posts
• Send feedback to Apple
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Get method name list
_methodDescription (located in UIKitCore)
import UIKit
let selector = Selector("_methodDescription")
let names = scrollView.perform(selector)
print(names)
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Get method name list
• Runtime Header
• p-x9/swift-objc-dump9
9 https://github.com/p-x9/swift-objc-dump
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Read stacktrace
• You can find methods
around breakpoint.
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Find SNS posts
• Survey the SNS landscape
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UIReturnKeyType(rawValue: 126)
textField.returnKeyType = UIReturnKeyType(rawValue: 126)!
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Send feedback to Apple
• Apple sometimes publicizes the API after receiving our feedback.
• Write feedback about usecases and APIs.
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Recap
• Perform
• Usecase
• Find
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Next steps
• Thinking about backend everytime.
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Thank you
• Special thanks
• @p_x9
• Guilherme Rosado
Martins
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References
https://www.jacklandrin.com/2018/05/16/method-in-objective-c-messgae-
passing/
https://xta0.me/2023/06/28/Swift-modules-1.html
https://www.kodeco.com/295-swizzling-in-ios-11-with-
uidebugginginformationoverlay/
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