# 不一样的动态化能力

> 对于热修复，对于大多数公司来说都是可望而不可及的技术手段。热修复对于线上问题是杀手锏级别项目。Android 热修复方案很多，典型的属微信的 `Tinker` 莫属，而苹果公司对于安全的要求非常高，所以一些动态调用的能力都会被封杀，这篇文章主要研究下 iOS 端的热修复技术方案。


## 热修复方案

- 将下发的原生代码，通过自己实现的代码解析引擎，将代码转换为AST树，然后存储在相关的模型里面，在通过一个上下文注入到runtime里面，当runtime回调到当前函数的时候，上下文从存储的相关模型取出各个参数，然后放到当前堆栈里面去执行相关的逻辑，执行问之后，在返回之前调用的地方，这里跟腾讯的OCS有点像.

- JSPatch：加加密，多混淆，关键词替换。（其实重要封杀的是respondsToSelector:, performSelector:, method_exchangeImplementations() 这些函数，然后现在aop、hook、jspatch 都是离不开这些函数的。解决方案将 动态能力的 API 替换名字：而是本地已经处理好，写到代码的静态变量里面，执行的时候去按照相应的解密方法去解密，然后得到 respondsToSelector:,  再去执行）

- 几大app中的方案都是自己研发的，不过大同小异，有比较多的是从编译器层面出发，直接把写的代码编译好，然后自己再写解析器解析执行

- lua kit：https://github.com/alibaba/LuaViewSDK；https://alibaba.github.io/LuaViewSDK/guide.html

其实重要封杀的是respondsToSelector:, performSelector:, method_exchangeImplementations() 这些函数，然后现在aop、hook、jspatch 都是离不开这些函数的。


## 思路

`JavaScriptCore` 是苹果给开发者操作 Javascript 的一个库，因此使用 JavaScriptCore 基本不存在问题。另外做热修复的基本思路就是在某个类执行某个类方法、某个类的对象执行某个对象方法的时候做一些处理。所以这里涉及到几个因素：类、类对象、类方法、实例方法、方法执行前、方法执行后、方法完全替换。 Objective-C 有运行时特性，所以可以很容易实现上面的几个点，但是直接使用 Runtime 会比较麻烦，这时候就不得不提一下一个面向切面编程的开源库-[Aspects](https://github.com/steipete/Aspects)。


所以剩下来的事情就是将 Aspects 的几个能力暴露给 JavascriptCore 对象。然后 App 在启动的时候去调用热修复接口，拿到修复的字符串，然后给 JavascriptCore 对象，然后 Javascript 对象去执行拿到的热修复的字符串，这样子整个流程下来，当我们去进入某个页面或者调用某个功能的时候，发现 A 类的 methodA 方法有问题，我们下发了热修复代码，就可以在 methodA 的前后加入逻辑，甚至是完全替换。


## 代码实现

<details>
<summary>FixManager</summary>

```Objective-C
#import <Foundation/Foundation.h>
#import "Aspects.h"
#import <objc/runtime.h>
#import <JavaScriptCore/JavaScriptCore.h>

NS_ASSUME_NONNULL_BEGIN

@interface FixManager : NSObject

+ (FixManager *)sharedInstance;
+ (void)fixIt;
+ (void)evalString:(NSString *)javascriptString;

@end

NS_ASSUME_NONNULL_END


#import "FixManager.h"

@implementation FixManager

+ (FixManager *)sharedInstance
{
    static FixManager *manager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        manager = [[self alloc] init];
    });
    return manager;
}


+ (JSContext *)context
{
    static JSContext *_context;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _context = [[JSContext alloc] init];
        [_context setExceptionHandler:^(JSContext *context, JSValue *exception) {
            NSLog(@"Ooops, %@", exception);
        }];
    });
    return _context;
}

+ (void)fixIt
{
    [self context][@"fixInstanceMethodBefore"] = ^(NSString *instanceName, NSString *selectorName, JSValue *fixImpl){
        [self _fixWithMethod:NO
            aspectionOptions:AspectPositionBefore instanceName:instanceName selectorName:selectorName fixImpl:fixImpl];
    };
    
    [self context][@"fixInstanceMethodReplace"] = ^(NSString *instanceName, NSString *selectorName, JSValue *fixImpl) {
        [self _fixWithMethod:NO aspectionOptions:AspectPositionInstead instanceName:instanceName selectorName:selectorName fixImpl:fixImpl];
    };
    
    [self context][@"fixInstanceMethodAfter"] = ^(NSString *instanceName, NSString *selectorName, JSValue *fixImpl) {
        [self _fixWithMethod:NO aspectionOptions:AspectPositionAfter instanceName:instanceName selectorName:selectorName fixImpl:fixImpl];
    };
    
    [self context][@"fixClassMethodBefore"] = ^(NSString *instanceName, NSString *selectorName, JSValue *fixImpl) {
        [self _fixWithMethod:YES aspectionOptions:AspectPositionBefore instanceName:instanceName selectorName:selectorName fixImpl:fixImpl];
    };
    
    [self context][@"fixClassMethodReplace"] = ^(NSString *instanceName, NSString *selectorName, JSValue *fixImpl) {
        [self _fixWithMethod:YES aspectionOptions:AspectPositionInstead instanceName:instanceName selectorName:selectorName fixImpl:fixImpl];
    };
    
    [self context][@"fixClassMethodAfter"] = ^(NSString *instanceName, NSString *selectorName, JSValue *fixImpl) {
        [self _fixWithMethod:YES aspectionOptions:AspectPositionAfter instanceName:instanceName selectorName:selectorName fixImpl:fixImpl];
    };
    
    [self context][@"runClassWithNoParamter"] = ^id(NSString *className, NSString *selectorName) {
        return [self _runClassWithClassName:className selector:selectorName obj1:nil obj2:nil];
    };
    
    [self context][@"runClassWith1Paramter"] = ^id(NSString *className, NSString *selectorName, id obj1) {
        return [self _runClassWithClassName:className selector:selectorName obj1:obj1 obj2:nil];
    };
    
    [self context][@"runClassWith2Paramters"] = ^id(NSString *className, NSString *selectorName, id obj1, id obj2) {
        return [self _runClassWithClassName:className selector:selectorName obj1:obj1 obj2:obj2];
    };
    
    [self context][@"runVoidClassWithNoParamter"] = ^(NSString *className, NSString *selectorName) {
        [self _runClassWithClassName:className selector:selectorName obj1:nil obj2:nil];
    };
    
    [self context][@"runVoidClassWith1Paramter"] = ^(NSString *className, NSString *selectorName, id obj1) {
        [self _runClassWithClassName:className selector:selectorName obj1:obj1 obj2:nil];
    };
    
    [self context][@"runVoidClassWith2Paramters"] = ^(NSString *className, NSString *selectorName, id obj1, id obj2) {
        [self _runClassWithClassName:className selector:selectorName obj1:obj1 obj2:obj2];
    };
    
    [self context][@"runInstanceWithNoParamter"] = ^id(id instance, NSString *selectorName) {
        return [self _runInstanceWithInstance:instance selector:selectorName obj1:nil obj2:nil];
    };
    
    [self context][@"runInstanceWith1Paramter"] = ^id(id instance, NSString *selectorName, id obj1) {
        return [self _runInstanceWithInstance:instance selector:selectorName obj1:obj1 obj2:nil];
    };
    
    [self context][@"runInstanceWith2Paramters"] = ^id(id instance, NSString *selectorName, id obj1, id obj2) {
        return [self _runInstanceWithInstance:instance selector:selectorName obj1:obj1 obj2:obj2];
    };
    
    [self context][@"runVoidInstanceWithNoParamter"] = ^(id instance, NSString *selectorName) {
        [self _runInstanceWithInstance:instance selector:selectorName obj1:nil obj2:nil];
    };
    
    [self context][@"runVoidInstanceWith1Paramter"] = ^(id instance, NSString *selectorName, id obj1) {
        [self _runInstanceWithInstance:instance selector:selectorName obj1:obj1 obj2:nil];
    };
    
    [self context][@"runVoidInstanceWith2Paramters"] = ^(id instance, NSString *selectorName, id obj1, id obj2) {
        [self _runInstanceWithInstance:instance selector:selectorName obj1:obj1 obj2:obj2];
    };
    
    [self context][@"runInvocation"] = ^(NSInvocation *invocation) {
        [invocation invoke];
    };
    
    // helper：将 JS 的 console.log 用 Native Log 替换
    [[self context] evaluateScript:@"var console = {}"];
    [self context][@"console"][@"log"] = ^(id message) {
        NSLog(@"Javascript log: %@",message);
    };
    
}

+ (void)_fixWithMethod:(BOOL)isClassMethod aspectionOptions:(AspectOptions)option instanceName:(NSString *)instanceName selectorName:(NSString *)selectorName fixImpl:(JSValue *)fixImpl
{
    Class klass = NSClassFromString(instanceName);
    if (isClassMethod) {
        klass = object_getClass(klass);
    }
    SEL sel = NSSelectorFromString(selectorName);
    [klass aspect_hookSelector:sel withOptions:option usingBlock:^(id<AspectInfo> aspectInfo){
        [fixImpl callWithArguments:@[aspectInfo.instance, aspectInfo.originalInvocation, aspectInfo.arguments]];
    } error:nil];
}

+ (id)_runClassWithClassName:(NSString *)className selector:(NSString *)selector obj1:(id)obj1 obj2:(id)obj2
{
    Class klass = NSClassFromString(className);
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    return [klass performSelector:NSSelectorFromString(selector) withObject:obj1 withObject:obj2];
#pragma clang diagnostic pop
}


+ (id)_runInstanceWithInstance:(id)instance selector:(NSString *)selector obj1:(id)obj1 obj2:(id)obj2
{
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    return [instance performSelector:NSSelectorFromString(selector) withObject:obj1 withObject:obj2];
#pragma clang diagnostic pop
}


+ (void)evalString:(NSString *)javascriptString
{
    [[self context] evaluateScript:javascriptString];
}

@end
```
</details>


  





<details>
<summary>BugProtector</summary>

```Objective-C
#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface BugProtector : NSObject

+ (instancetype)sharedInstance;

+ (void)getFixScript:(NSString *)scriptText;

@end

NS_ASSUME_NONNULL_END

#import "BugProtector.h"
#import "FixManager.h"

@interface BugProtector ()

@end

@implementation BugProtector

static BugProtector *_sharedInstance = nil;

#pragma mark - life cycle
+ (instancetype)sharedInstance
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        //because has rewrited allocWithZone  use NULL avoid endless loop lol.
        _sharedInstance = [[super allocWithZone:NULL] init];
        [FixManager fixIt];
    });
    
    return _sharedInstance;
}

+ (FixManager *)fixManager
{
    static FixManager *_manager;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _manager = [FixManager sharedInstance];
    });
    return _manager;
}

+ (id)allocWithZone:(struct _NSZone *)zone
{
    return [BugProtector sharedInstance];
}

+ (instancetype)alloc
{
    return [BugProtector sharedInstance];
}

- (id)copy
{
    return self;
}

- (id)mutableCopy
{
    return self;
}

- (id)copyWithZone:(struct _NSZone *)zone
{
    return self;
}

#ifdef DEBUG
- (void)dealloc
{
    NSLog(@"%s",__func__);
}
#endif


#pragma mark - public Method
+ (void)getFixScript:(NSString *)scriptText
{
    [FixManager evalString:scriptText];
}

@end
```
</details>


完整的 [Demo](https://github.com/FantasticLBP/BlogDemos/tree/master/HotFix) 可以点此查看链接.


## 未完，待续