热修复开发历程
最近一直在复习基础和整合知识文档，这里主要记录一下公司项目中采用的热修复技术。最早接触热修复正是JSPatch大行其道的时候，可惜愉快的使用不长时间就因为种种原因被苹果审核彻底封禁了。被封后笔者也采用了网上寻找到的诸如混淆关键字等策略，可惜最后也是无果而终。机缘巧合下接触到了AOP（面向切面编程），后来经过查询整合和对JSPatch的技术进行借鉴，最后封装了现在使用的热修复库。
什么是AOP
网上有很多资料，本篇主要阐述热修复的原理，AOP方面的知识可以参考笔者转载的一篇技术贴转：Aspects深度解析-iOS面向切面编程
热修复思想
这里主要借鉴JSPatch的思想，采用网络下发JS代码，并借用JavaScriptCore进行解析后调用AOP经典三方库Aspects在函数执行阶段进行插入、修改等操作，具体可以参考如下核心代码
核心代码
+ (Felix *)sharedInstance
{
static Felix *sharedInstance = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedInstance = [[self alloc] init];
});
return sharedInstance;
}
+ (void)evalString:(NSString *)javascriptString
{
[[self context] evaluateScript:javascriptString];
}
+ (JSContext *)context
{
static JSContext *_context;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_context = [[JSContext alloc] init];
[_context setExceptionHandler:^(JSContext *context, JSValue *value) {
NSLog(@"Oops: %@", value);
}];
});
return _context;
}
+ (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 arguments:(NSArray *)arguments
{
Class class = NSClassFromString(className);
SEL sel = NSSelectorFromString(selector);
NSMethodSignature *methodSignature = [class methodSignatureForSelector:sel];
return [self safePerformAction:sel target:class params:arguments methodSig:methodSignature];
}
+(id)_runInstanceWithInstance:(id)instance selector:(NSString *)selector arguments:(NSArray *)arguments
{
SEL sel = NSSelectorFromString(selector);
NSMethodSignature *methodSignature = [[instance class] instanceMethodSignatureForSelector:sel];
return [self safePerformAction:sel target:instance params:arguments methodSig:methodSignature];
}
+ (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][@"runClassMethod"] = ^id(NSString *className, NSString *selectorName, NSArray * _Nullable params) {
return [self _runClassWithClassName:className selector:selectorName arguments:params];
};
[self context][@"runInstanceMethod"] = ^id(id instance, NSString *selectorName, NSArray * _Nullable params) {
return [self _runInstanceWithInstance:instance selector:selectorName arguments:params];
};
[self context][@"runInstanceWithKeyPath"] = ^id(id instance, NSString *keyPath, NSString *selector, NSArray * _Nullable params) {
id subInstance = [instance valueForKeyPath:keyPath];
return [self _runInstanceWithInstance:subInstance selector:selector arguments:params];
};
[self context][@"runInvocation"] = ^(NSInvocation *invocation) {
[invocation invoke];
};
[self context][@"runInvocationWithParams"] = ^(NSInvocation *invocation, NSArray * _Nullable params) {
if (params && [params isKindOfClass:[NSArray class]]) {
for (int i=0; i<params.count; i++) {
id value = params[i];
[self setArgument:invocation value:value atIndex:i+2];
}
}
[invocation invoke];
};
[self context][@"runInvocationWithReturn"] = ^(NSInvocation *invocation, id returnValue) {
[invocation setReturnValue:&returnValue];
};
[self context][@"valueForKeyPath"] = ^id(id instance, NSString *keyPath) {
id value = [instance valueForKeyPath:keyPath];
return [JSValue valueWithObject:value inContext:[JSContext currentContext]];
};
[self context][@"setValueForKeyPath"] = ^(id instance, NSString *keyPath, id value) {
[instance setValue:value forKeyPath:keyPath];
};
[self context][@"CGRectMake"] = ^NSValue *(CGFloat x,CGFloat y,CGFloat width,CGFloat height) {
return @(CGRectMake(x, y, width, height));
};
[self context][@"CGSizeMake"] = ^NSValue *(CGFloat width,CGFloat height) {
return @(CGSizeMake(width, height));
};
[self context][@"CGPointMake"] = ^NSValue *(CGFloat x,CGFloat y) {
return @(CGPointMake(x, y));
};
// log方法
[self context][@"log"] = ^(id message) {
NSLog(@"Javascript log: %@",message);
};
}
+(void)setArgument:(NSInvocation *)invocation value:(id)value atIndex:(NSInteger)index
{
const char *c = [invocation.methodSignature getArgumentTypeAtIndex:index];
if (strcmp(c, "@") == 0) {
[invocation setArgument:&value atIndex:index];
}
else if(strcmp(c, "q") == 0) {
long argu = [value longValue];
[invocation setArgument:&argu atIndex:index];
}
else if (strcmp(c, "l") == 0) {
long long argu = [value longLongValue];
[invocation setArgument:&argu atIndex:index];
}
else if (strcmp(c, "d") == 0) {
double argu = [value doubleValue];
[invocation setArgument:&argu atIndex:index];
}
else if (strcmp(c, "f") == 0) {
float argu = [value floatValue];
[invocation setArgument:&argu atIndex:index];
}
else if (strcmp(c, "B") == 0) {
bool argu = [value boolValue];
[invocation setArgument:&argu atIndex:index];
}
else if (strcmp(c, "s") == 0) {
short argu = [value shortValue];
[invocation setArgument:&argu atIndex:index];
}
else if (strcmp(c, "c") == 0) {
char argu = [value charValue];
[invocation setArgument:&argu atIndex:index];
}
else {
[invocation setArgument:&value atIndex:index];
}
}
+ (id)safePerformAction:(SEL)action target:(id)target params:(NSArray *)params methodSig:(NSMethodSignature *)medSig
{
NSMethodSignature* methodSig;
if (medSig) {
methodSig = medSig;
}
else {
methodSig = [target methodSignatureForSelector:action];
}
if(methodSig == nil) {
return nil;
}
const char* retType = [methodSig methodReturnType];
if (strcmp(retType, @encode(void)) == 0) {
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setTarget:target];
[self addInvocation:invocation params:params isBlock:action==nil];
if (action) {
[invocation setSelector:action];
}
[invocation invoke];
return nil;
}
if (strcmp(retType, @encode(NSInteger)) == 0) {
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setTarget:target];
[self addInvocation:invocation params:params isBlock:action==nil];
if (action) {
[invocation setSelector:action];
}
[invocation invoke];
NSInteger result = 0;
[invocation getReturnValue:&result];
return @(result);
}
if (strcmp(retType, @encode(BOOL)) == 0) {
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setTarget:target];
[self addInvocation:invocation params:params isBlock:action==nil];
if (action) {
[invocation setSelector:action];
}
[invocation invoke];
BOOL result = 0;
[invocation getReturnValue:&result];
return @(result);
}
if (strcmp(retType, @encode(CGFloat)) == 0) {
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setTarget:target];
[self addInvocation:invocation params:params isBlock:action==nil];
if (action) {
[invocation setSelector:action];
}
[invocation invoke];
CGFloat result = 0;
[invocation getReturnValue:&result];
return @(result);
}
if (strcmp(retType, @encode(NSUInteger)) == 0) {
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setTarget:target];
[self addInvocation:invocation params:params isBlock:action==nil];
if (action) {
[invocation setSelector:action];
}
[invocation invoke];
NSUInteger result = 0;
[invocation getReturnValue:&result];
return @(result);
}
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setTarget:target];
[self addInvocation:invocation params:params isBlock:action==nil];
if (action) {
[invocation setSelector:action];
}
[invocation invoke];
void *obj;
[invocation getReturnValue:&obj];
return (__bridge NSObject *)obj;
}
+(void)addInvocation:(NSInvocation *)invocation params:(NSArray *)params isBlock:(BOOL)isBlock
{
if (!params || ![params isKindOfClass:[NSArray class]]) {
return;
}
for (int i=0; i<params.count; i++) {
[self setArgument:invocation value:params[i] atIndex:isBlock?i+1:i+2];
}
}
上面主要是一些常用的方法，可以实现诸如调用类方法、实例方法，KVC方式获取属性等及基本操作，其他的复杂操作诸位可以借鉴这些实现方式自行添加
JS代码下发
考虑到代码下发阶段被恶意篡改等安全问题，笔者主要将JS源码MD5操作后采用RSA非对称加密生成秘钥文件，然后将秘钥文件和JS源码共同下发，执行阶段在进行秘钥比对，如果核实通过执行
总结和不足
1、热修复虽然实现了一些基础方法，但是如创建block、多线程操作等因为时间原因一直没有进行迭代优化
2、公司采用的私有cocoapods部署，一直没有机会放到github进行公开
3、Aspects作为优秀的AOP库，但由于时间过于悠久，执行效率有些低下，后期有机会可以使用Stinger进行重构
