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NSExceptional/HookUIApplicationMain.m

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Hooking UIApplicationMain in Swift or Objc apps with Fishhook

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HookUIApplicationMain.m

	// UIApplicationMain accepts Swift.String in Swift apps; a C forward declaration is needed
	struct SwiftString {
	uint8_t reserved[16];
	};
	typedefstruct SwiftString SwiftString;

	int (orig_UIApplicationMain_objc)(int argc,char argv[],NSString _,NSString delegateClassName) =nil;
	int (orig_UIApplicationMain_swift)(int argc,char argv[], SwiftString _, SwiftString delegateClassName) =nil;
	NSString (FoundationBridgeSwiftStringToObjC)(SwiftString str) =nil;

	// Our hooks //

	staticintUIApplicationMain_objc(int argc,char argv[],NSString _,NSString *delegateClassName) {
	Class appDelegateClass =NSClassFromString(delegateClassName)];
	// ...
	returnorig_UIApplicationMain_objc(argc, argv, _, delegateClassName);
	}

	staticintUIApplicationMain_swift(int argc,char *argv[], SwiftString _, SwiftString delegate) {
	NSString *delegateClassName =FoundationBridgeSwiftStringToObjC(delegate);
	Class appDelegateClass =NSClassFromString(delegateClassName)];
	// ...
	returnorig_UIApplicationMain_swift(argc, argv, _, delegate);
	}

	// Hooking logic //

	voidctor() {
	// UIApplicationMain objc
	__unusedBOOL didHookObjcMain =flex_rebind_symbols((struct rebinding[1]) {{
	"UIApplicationMain",
	(void *)UIApplicationMain_objc,
	(void **)&orig_UIApplicationMain_objc
	}},1) ==0;

	// UIApplicationMain Swift shim
	void *mainBinary =dlopen(NSBundle.mainBundle.executablePath.UTF8String, RTLD_LAZY);
	void *swiftmain =dlsym(mainBinary,"$s5UIKit17UIApplicationMainys5Int32VAD_SpySpys4Int8VGGSgSSSgAJtF");
	// For convering Swift.String (a struct) to an NSString
	void *stringBridge =dlsym(mainBinary,"$sSS10FoundationE19_bridgeToObjectiveCSo8NSStringCyF");

	// If the shim exists, hook it as well. Only one will be called when using Fishhook
	if (swiftmain && stringBridge) {
	// For convering Swift.String (a struct) to an NSString
	FoundationBridgeSwiftStringToObjC = stringBridge;
	// Hook UIApplicationMain(Int32, UnsafeMutablePointer<…>?, Swift.String?, Swift.String?) -> Int32
	__unusedBOOL didHookSwiftMain =rebind_symbols((struct rebinding[1]) {{
	"$s5UIKit17UIApplicationMainys5Int32VAD_SpySpys4Int8VGGSgSSSgAJtF",
	(void *)UIApplicationMain_swift,
	(void **)&orig_UIApplicationMain_swift
	}},1) ==0;
	}
	}

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NSExceptional/HookUIApplicationMain.m