JSPatch 源码解析(一)

1.前言

前一段时间在公司做了一个iOS热补丁的模块，就用到了JSPatch框架,期间有了解过一些关于框架的源码分析的博客：

1.JSPatch学习:JSPatch核心和实现原理分析

2.JSPatch defineProtocol部分实现详解

思考再三还是决定自己调试了解一下整体的实现机制。

2.准备工具

3.项目文件

3.1项目文件图

3.2具体文件分析

  • JPEngine.m 核心的Native端实现。
  • JSpatch.js 核心的js端实现。
  • Extensions 扩展的方法提供给js端调用，内部是OC实现。
  • Loader 一套热补丁动态更新补丁脚本的客户端实现，需要配合服务端才能实现整个更新框架。（本文不对此作多赘述）

4.调试分析

4.1调用代码

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[JPEngine startEngine];
NSString *sourcePath = [[NSBundle mainBundle] pathForResource:@"demo" ofType:@"js"];
NSString *script = [NSString stringWithContentsOfFile:sourcePath encoding:NSUTF8StringEncoding error:nil];
[JPEngine evaluateScript:script];

4.2 JPEngine初始化

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[JPEngine startEngine];

我们来看看具体的代码实现，

  • 代码片段一：
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+ (void)startEngine
{
    if (![JSContext class] || _context) {
        return;
    }
    
    JSContext *context = [[JSContext alloc] init];
    
    context[@"_OC_defineClass"] = ^(NSString *classDeclaration, JSValue *instanceMethods, JSValue *classMethods) {
        return defineClass(classDeclaration, instanceMethods, classMethods);
    };

    context[@"_OC_defineProtocol"] = ^(NSString *protocolDeclaration, JSValue *instProtocol, JSValue *clsProtocol) {
        return defineProtocol(protocolDeclaration, instProtocol,clsProtocol);
    };
    
    /*.... 分块分析，暂时省略以下代码*/
}

_content 为JSContect的实例，根据苹果官方文档 :

我们知道JSContext为js的执行环境。因此例如：
context[@"_OC_defineProtocol"]=block实现这样的调用就很好的理解为为js的上下文注入了全局的_OC_defineProtocol方法，而具体的实现对应着Native端的block的实现。

  • 代码片段二：
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NSString *path = [[NSBundle bundleForClass:[self class]] pathForResource:@"JSPatch" ofType:@"js"];
NSAssert(path, @"can't find JSPatch.js");
NSString *jsCore = [[NSString alloc] initWithData:[[NSFileManager defaultManager] contentsAtPath:path] encoding:NSUTF8StringEncoding];
    
 if ([_context respondsToSelector:@selector(evaluateScript:withSourceURL:)]) {
        [_context evaluateScript:jsCore withSourceURL:[NSURL URLWithString:@"JSPatch.js"]];
 } else {
        [_context evaluateScript:jsCore];
 }

加载核心的JSPatch.js代码完成初始化，具体js代码后续具体调用再作分析。

4.3具体修复代码

我们来看看Demo的修复代码：

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defineClass('JPViewController', {
  handleBtn: function(sender) {
    var tableViewCtrl = JPTableViewController.alloc().init()
    self.navigationController().pushViewController_animated(tableViewCtrl, YES)
  }
})

调试看看执行步骤：

4.3.1 首先执行global.defineClass (js端)

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global.defineClass = function(declaration, properties, instMethods, clsMethods)

我们断点到var ret = _OC_defineClass(declaration, newInstMethods, newClsMethods)处，查看局部变量表
会发现newInstMethods newClsMethods均被赋值，且其中每个实例或类方法的js对象被修改添加参数的个数的说明，只是好奇为什么需要加入参数个数的说明呢？？？

4.3.2 执行_OC_defineClass (js端 -> Native端)

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context[@"_OC_defineClass"] = ^(NSString *classDeclaration, JSValue *instanceMethods, JSValue *classMethods) {
       return defineClass(classDeclaration, instanceMethods, classMethods);
   };

实际执行的是Native的 static NSDictionary *defineClass(NSString *classDeclaration, JSValue *instanceMethods, JSValue *classMethods) 方法,以下分代码片段解析。

  • 代码片段一：
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NSScanner *scanner = [NSScanner scannerWithString:classDeclaration];
    
    NSString *className;
    NSString *superClassName;
    NSString *protocolNames;
    [scanner scanUpToString:@":" intoString:&className];
    if (!scanner.isAtEnd) {
        scanner.scanLocation = scanner.scanLocation + 1;
        [scanner scanUpToString:@"<" intoString:&superClassName];
        if (!scanner.isAtEnd) {
            scanner.scanLocation = scanner.scanLocation + 1;
            [scanner scanUpToString:@">" intoString:&protocolNames];
        }
    }
    
    if (!superClassName) superClassName = @"NSObject";
    className = trim(className);
    superClassName = trim(superClassName);
    
    NSArray *protocols = [protocolNames length] ? [protocolNames componentsSeparatedByString:@","] : nil;
    
    Class cls = NSClassFromString(className);
    if (!cls) {
        Class superCls = NSClassFromString(superClassName);
        if (!superCls) {
            NSCAssert(NO, @"can't find the super class %@", superClassName);
            return @{@"cls": className};
        }
        cls = objc_allocateClassPair(superCls, className.UTF8String, 0);
        objc_registerClassPair(cls);
    }

    if (protocols.count > 0) {
        for (NSString* protocolName in protocols) {
            Protocol *protocol = objc_getProtocol([trim(protocolName) cStringUsingEncoding:NSUTF8StringEncoding]);
            class_addProtocol (cls, protocol);
        }
    }

通过传递的classDeclaration解析相应的className,superClassName,protocols,

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//1.
cls = objc_allocateClassPair(superCls, className.UTF8String, 0);
objc_registerClassPair(cls);
 
 //2.
 if (protocols.count > 0) {
        for (NSString* protocolName in protocols) {
            Protocol *protocol = objc_getProtocol([trim(protocolName) cStringUsingEncoding:NSUTF8StringEncoding]);
            class_addProtocol (cls, protocol);
        }
    }

1.运行期间创建一个新类，并完成注册. 2.遍历协议名，依此初始化并完成对类的协议的添加。

  • 代码片段二：
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for (int i = 0; i < 2; i ++) {
        BOOL isInstance = i == 0;
        JSValue *jsMethods = isInstance ? instanceMethods: classMethods;
        
        Class currCls = isInstance ? cls: objc_getMetaClass(className.UTF8String);
        NSDictionary *methodDict = [jsMethods toDictionary];
        for (NSString *jsMethodName in methodDict.allKeys) {
            JSValue *jsMethodArr = [jsMethods valueForProperty:jsMethodName];
            int numberOfArg = [jsMethodArr[0] toInt32];
            NSString *selectorName = convertJPSelectorString(jsMethodName);
            
            if ([selectorName componentsSeparatedByString:@":"].count - 1 < numberOfArg) {
                selectorName = [selectorName stringByAppendingString:@":"];
            }
            
            JSValue *jsMethod = jsMethodArr[1];
            if (class_respondsToSelector(currCls, NSSelectorFromString(selectorName))) {
                overrideMethod(currCls, selectorName, jsMethod, !isInstance, NULL);
            } else {
                BOOL overrided = NO;
                for (NSString *protocolName in protocols) {
                    char *types = methodTypesInProtocol(protocolName, selectorName, isInstance, YES);
                    if (!types) types = methodTypesInProtocol(protocolName, selectorName, isInstance, NO);
                    if (types) {
                        overrideMethod(currCls, selectorName, jsMethod, !isInstance, types);
                        free(types);
                        overrided = YES;
                        break;
                    }
                }
                if (!overrided) {
                    if (![[jsMethodName substringToIndex:1] isEqualToString:@"_"]) {
                        NSMutableString *typeDescStr = [@"@@:" mutableCopy];
                        for (int i = 0; i < numberOfArg; i ++) {
                            [typeDescStr appendString:@"@"];
                        }
                        overrideMethod(currCls, selectorName, jsMethod, !isInstance, [typeDescStr cStringUsingEncoding:NSUTF8StringEncoding]);
                    }
                }
            }
        }
    }
  • 遍历传递过过来的实例方法，类方法的js实例，然后依次遍历方法字典，完成方法名js命名到native命名的转换。
  • 通过转换后的方法名，用class_respondsToSelector判断是否该类的方法列表中是否已经存在该方法的实现，存在即调用overrideMethod(currCls, selectorName, jsMethod, !isInstance, NULL);覆盖方法实现。

  • 如果类的方法列表中不存在该方法的实现，则通过实现的协议的列表查找，依次判断方法是否在协议的实现方法中,如果以上都不是说明是新添加的方法.

  • 代码片段三：

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#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wundeclared-selector"
    class_addMethod(cls, @selector(getProp:), (IMP)getPropIMP, "@@:@");
    class_addMethod(cls, @selector(setProp:forKey:), (IMP)setPropIMP, "v@:@@");
#pragma clang diagnostic pop

添加类的getProp:``setProp:forKey:的方法及实现。

  • 代码片段四：
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static void overrideMethod(Class cls, NSString *selectorName, JSValue *function, BOOL isClassMethod, const char *typeDescription)
{
    SEL selector = NSSelectorFromString(selectorName);
    
    if (!typeDescription) {
        Method method = class_getInstanceMethod(cls, selector);
        typeDescription = (char *)method_getTypeEncoding(method);
    }
    
    IMP originalImp = class_respondsToSelector(cls, selector) ? class_getMethodImplementation(cls, selector) : NULL;
    
    IMP msgForwardIMP = _objc_msgForward;
    #if !defined(__arm64__)
        if (typeDescription[0] == '{') {
            //In some cases that returns struct, we should use the '_stret' API:
            //http://sealiesoftware.com/blog/archive/2008/10/30/objc_explain_objc_msgSend_stret.html
            //NSMethodSignature knows the detail but has no API to return, we can only get the info from debugDescription.
            NSMethodSignature *methodSignature = [NSMethodSignature signatureWithObjCTypes:typeDescription];
            if ([methodSignature.debugDescription rangeOfString:@"is special struct return? YES"].location != NSNotFound) {
                msgForwardIMP = (IMP)_objc_msgForward_stret;
            }
        }
    #endif

    class_replaceMethod(cls, selector, msgForwardIMP, typeDescription);

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wundeclared-selector"
    if (class_getMethodImplementation(cls, @selector(forwardInvocation:)) != (IMP)JPForwardInvocation) {
        IMP originalForwardImp = class_replaceMethod(cls, @selector(forwardInvocation:), (IMP)JPForwardInvocation, "v@:@");
        class_addMethod(cls, @selector(ORIGforwardInvocation:), originalForwardImp, "v@:@");
    }
#pragma clang diagnostic pop

    if (class_respondsToSelector(cls, selector)) {
        NSString *originalSelectorName = [NSString stringWithFormat:@"ORIG%@", selectorName];
        SEL originalSelector = NSSelectorFromString(originalSelectorName);
        if(!class_respondsToSelector(cls, originalSelector)) {
            class_addMethod(cls, originalSelector, originalImp, typeDescription);
        }
    }
    
    NSString *JPSelectorName = [NSString stringWithFormat:@"_JP%@", selectorName];
    SEL JPSelector = NSSelectorFromString(JPSelectorName);

    _initJPOverideMethods(cls);
    _JSOverideMethods[cls][JPSelectorName] = function;
    
    class_addMethod(cls, JPSelector, msgForwardIMP, typeDescription);
}

核心的替换添加方法实现的方法：

  • 把原始的方法的实现替换为_objc_msgForward,即该方法的调用会走消息转发的路径.
  • 类的forwardInvocation:方法的实现被替换为JPForwardInvocation的实现
  • 添加的方法ORIGforwardInvocation指向原始的实现IMP.
  • 添加的方法ORIG+selector指向原始的实现的IMP.
  • 添加_JP+selector指向新的函数的实现.

上述代码只是讲解了替换添加方法的实现，而新的实现方法是一个个js的对象，如何关联到Native端的调用？后续会继续更新，分析 调用核心方法JPForwardInvocation,JPExtension等其他部分的实现，对于上述的分析有问题处欢迎及时指出，谢谢!

补充：4.3.1 中为什么需要加入参数个数的说明呢，与方法的签名有关，具体下次更新作分析！！！