oc 运行时消息转发的 aop
运行时的消息转发
https://www.cnblogs.com/feng9exe/p/10945712.html
其实在 objc-msg-x86_64.s 中包含了多个版本的 objc_msgSend 方法，它们是根据返回值的类型和调用者的类型分别处理的：
objc_msgSendSuper:向父类发消息，返回值类型为idobjc_msgSend_fpret:返回值类型为 floating-point，其中包含objc_msgSend_fp2ret入口处理返回值类型为long double的情况objc_msgSend_stret:返回值为结构体objc_msgSendSuper_stret:向父类发消息，返回值类型为结构体
面向对象的消息转发处理
Runtime系统会向对象发送methodSignatureForSelector:消息，并取到返回的方法签名用于生成NSInvocation对象。为接下来的完整的消息转发生成一个 NSMethodSignature对象。NSMethodSignature 对象会被包装成 NSInvocation 对象，forwardInvocation: 方法里就可以对 NSInvocation 进行处理了。
在上一篇中我们分析过了，在objc_msgSend函数查找IMP的过程中，如果在父类也没有找到相应的IMP，那么就会开始执行_class_resolveMethod方法，如果不是元类，就执行_class_resolveInstanceMethod，如果是元类，执行_class_resolveClassMethod。在这个方法中，允许开发者动态增加方法实现。这个阶段一般是给@dynamic属性变量提供动态方法的。
基于消息转发的 AOP
1. 将原方法指向消息转发逻辑
static void aspect_prepareClassAndHookSelector(NSObject *self, SEL selector, NSError **error) {
NSCParameterAssert(selector);
Class klass = aspect_hookClass(self, error);
Method targetMethod = class_getInstanceMethod(klass, selector);
IMP targetMethodIMP = method_getImplementation(targetMethod);
if (!aspect_isMsgForwardIMP(targetMethodIMP)) {
// Make a method alias for the existing method implementation, it not already copied.
const char *typeEncoding = method_getTypeEncoding(targetMethod);
SEL aliasSelector = aspect_aliasForSelector(selector);
if (![klass instancesRespondToSelector:aliasSelector]) {
__unused BOOL addedAlias = class_addMethod(klass, aliasSelector, method_getImplementation(targetMethod), typeEncoding);
NSCAssert(addedAlias, @"Original implementation for %@ is already copied to %@ on %@", NSStringFromSelector(selector), NSStringFromSelector(aliasSelector), klass);
}
// We use forwardInvocation to hook in.
class_replaceMethod(klass, selector, aspect_getMsgForwardIMP(self, selector), typeEncoding);
AspectLog(@"Aspects: Installed hook for -[%@ %@].", klass, NSStringFromSelector(selector));
}
}
// Will undo the runtime changes made.
static void aspect_cleanupHookedClassAndSelector(NSObject *self, SEL selector) {
NSCParameterAssert(self);
NSCParameterAssert(selector);
Class klass = object_getClass(self);
BOOL isMetaClass = class_isMetaClass(klass);
if (isMetaClass) {
klass = (Class)self;
}
// Check if the method is marked as forwarded and undo that.
Method targetMethod = class_getInstanceMethod(klass, selector);
IMP targetMethodIMP = method_getImplementation(targetMethod);
if (aspect_isMsgForwardIMP(targetMethodIMP)) {
// Restore the original method implementation.
const char *typeEncoding = method_getTypeEncoding(targetMethod);
SEL aliasSelector = aspect_aliasForSelector(selector);
Method originalMethod = class_getInstanceMethod(klass, aliasSelector);
IMP originalIMP = method_getImplementation(originalMethod);
NSCAssert(originalMethod, @"Original implementation for %@ not found %@ on %@", NSStringFromSelector(selector), NSStringFromSelector(aliasSelector), klass);
class_replaceMethod(klass, selector, originalIMP, typeEncoding);
AspectLog(@"Aspects: Removed hook for -[%@ %@].", klass, NSStringFromSelector(selector));
}
// Deregister global tracked selector
aspect_deregisterTrackedSelector(self, selector);
// Get the aspect container and check if there are any hooks remaining. Clean up if there are not.
AspectsContainer *container = aspect_getContainerForObject(self, selector);
if (!container.hasAspects) {
// Destroy the container
aspect_destroyContainerForObject(self, selector);
// Figure out how the class was modified to undo the changes.
NSString *className = NSStringFromClass(klass);
if ([className hasSuffix:AspectsSubclassSuffix]) {
Class originalClass = NSClassFromString([className stringByReplacingOccurrencesOfString:AspectsSubclassSuffix withString:@""]);
NSCAssert(originalClass != nil, @"Original class must exist");
object_setClass(self, originalClass);
AspectLog(@"Aspects: %@ has been restored.", NSStringFromClass(originalClass));
// We can only dispose the class pair if we can ensure that no instances exist using our subclass.
// Since we don't globally track this, we can't ensure this - but there's also not much overhead in keeping it around.
//objc_disposeClassPair(object.class);
}else {
// Class is most likely swizzled in place. Undo that.
if (isMetaClass) {
aspect_undoSwizzleClassInPlace((Class)self);
}
}
}
}
static IMP aspect_getMsgForwardIMP(NSObject *self, SEL selector) {
IMP msgForwardIMP = _objc_msgForward;
#if !defined(__arm64__)
// As an ugly internal runtime implementation detail in the 32bit runtime, we need to determine of the method we hook returns a struct or anything larger than id.
// https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/LowLevelABI/000-Introduction/introduction.html
// https://github.com/ReactiveCocoa/ReactiveCocoa/issues/783
// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042e/IHI0042E_aapcs.pdf (Section 5.4)
Method method = class_getInstanceMethod(self.class, selector);
const char *encoding = method_getTypeEncoding(method);
BOOL methodReturnsStructValue = encoding[0] == _C_STRUCT_B;
if (methodReturnsStructValue) {
@try {
NSUInteger valueSize = 0;
NSGetSizeAndAlignment(encoding, &valueSize, NULL);
if (valueSize == 1 || valueSize == 2 || valueSize == 4 || valueSize == 8) {
methodReturnsStructValue = NO;
}
} @catch (NSException *e) {}
}
if (methodReturnsStructValue) {
msgForwardIMP = (IMP)_objc_msgForward_stret;
}
#endif
return msgForwardIMP;
}
2. hook 转发处理逻辑进行二次转发
static void aspect_swizzleForwardInvocation(Class klass) {
NSCParameterAssert(klass);
// If there is no method, replace will act like class_addMethod.
//把forwardInvocation的IMP替换成__ASPECTS_ARE_BEING_CALLED__
//class_replaceMethod返回的是原方法的IMP
IMP originalImplementation = class_replaceMethod(klass, @selector(forwardInvocation:), (IMP)__ASPECTS_ARE_BEING_CALLED__, "v@:@");
// originalImplementation不为空的话说明原方法有实现，添加一个新方法__aspects_forwardInvocation:指向了原来的originalImplementation，在__ASPECTS_ARE_BEING_CALLED__那里如果不能处理，判断是否有实现__aspects_forwardInvocation，有的话就转发。
if (originalImplementation) {
class_addMethod(klass, NSSelectorFromString(AspectsForwardInvocationSelectorName), originalImplementation, "v@:@");
}
AspectLog(@"Aspects: %@ is now aspect aware.", NSStringFromClass(klass));
}
static void __ASPECTS_ARE_BEING_CALLED__(__unsafe_unretained NSObject *self, SEL selector, NSInvocation *invocation) {
NSCParameterAssert(self);
NSCParameterAssert(invocation);
//获取原始的selector
SEL originalSelector = invocation.selector;
//获取带有aspects_xxxx前缀的方法
SEL aliasSelector = aspect_aliasForSelector(invocation.selector);
//替换selector
invocation.selector = aliasSelector;
//获取实例对象的容器objectContainer，这里是之前aspect_add关联过的对象
AspectsContainer *objectContainer = objc_getAssociatedObject(self, aliasSelector);
//获取获得类对象容器classContainer
AspectsContainer *classContainer = aspect_getContainerForClass(object_getClass(self), aliasSelector);
//初始化AspectInfo，传入self、invocation参数
AspectInfo *info = [[AspectInfo alloc] initWithInstance:self invocation:invocation];
NSArray *aspectsToRemove = nil;
// Before hooks.
//调用宏定义执行Aspects切片功能
//宏定义里面就做了两件事情，一个是执行了[aspect invokeWithInfo:info]方法，一个是把需要remove的Aspects加入等待被移除的数组中。
aspect_invoke(classContainer.beforeAspects, info);
aspect_invoke(objectContainer.beforeAspects, info);
// Instead hooks.
BOOL respondsToAlias = YES;
if (objectContainer.insteadAspects.count || classContainer.insteadAspects.count) {
aspect_invoke(classContainer.insteadAspects, info);
aspect_invoke(objectContainer.insteadAspects, info);
}else {
Class klass = object_getClass(invocation.target);
do {
if ((respondsToAlias = [klass instancesRespondToSelector:aliasSelector])) {
[invocation invoke];
break;
}
}while (!respondsToAlias && (klass = class_getSuperclass(klass)));
}
// After hooks.
aspect_invoke(classContainer.afterAspects, info);
aspect_invoke(objectContainer.afterAspects, info);
// If no hooks are installed, call original implementation (usually to throw an exception)
if (!respondsToAlias) {
invocation.selector = originalSelector;
SEL originalForwardInvocationSEL = NSSelectorFromString(AspectsForwardInvocationSelectorName);
if ([self respondsToSelector:originalForwardInvocationSEL]) {
((void( *)(id, SEL, NSInvocation *))objc_msgSend)(self, originalForwardInvocationSEL, invocation);
}else {
[self doesNotRecognizeSelector:invocation.selector];
}
}
// Remove any hooks that are queued for deregistration.
[aspectsToRemove makeObjectsPerformSelector:@selector(remove)];
}
#define aspect_invoke(aspects, info) \
for (AspectIdentifier *aspect in aspects) {\
[aspect invokeWithInfo:info];\
if (aspect.options & AspectOptionAutomaticRemoval) { \
aspectsToRemove = [aspectsToRemove?:@[] arrayByAddingObject:aspect]; \
} \
}
- (BOOL)invokeWithInfo:(id<AspectInfo>)info {
NSInvocation *blockInvocation = [NSInvocation invocationWithMethodSignature:self.blockSignature];
NSInvocation *originalInvocation = info.originalInvocation;
NSUInteger numberOfArguments = self.blockSignature.numberOfArguments;
// Be extra paranoid. We already check that on hook registration.
if (numberOfArguments > originalInvocation.methodSignature.numberOfArguments) {
AspectLogError(@"Block has too many arguments. Not calling %@", info);
return NO;
}
// The `self` of the block will be the AspectInfo. Optional.
if (numberOfArguments > 1) {
[blockInvocation setArgument:&info atIndex:1];
}
void *argBuf = NULL;
//把originalInvocation中的参数
for (NSUInteger idx = 2; idx < numberOfArguments; idx++) {
const char *type = [originalInvocation.methodSignature getArgumentTypeAtIndex:idx];
NSUInteger argSize;
NSGetSizeAndAlignment(type, &argSize, NULL);
if (!(argBuf = reallocf(argBuf, argSize))) {
AspectLogError(@"Failed to allocate memory for block invocation.");
return NO;
}
[originalInvocation getArgument:argBuf atIndex:idx];
[blockInvocation setArgument:argBuf atIndex:idx];
}
[blockInvocation invokeWithTarget:self.block];
if (argBuf != NULL) {
free(argBuf);
}
return YES;
}
我思故我在
