前言

JSPatch是一個非常棒的熱修復框架，10000+star！！！！！雖說2017年被蘋果封殺了，但是據我獲取到的有限的信息，大家還是偷偷摸摸混淆一下、改改類名繼續在使用。畢竟bug還是不可避免的，有了JSPatch萬一出了問題我們還是能夠搶救一下的。一些實現細節bang哥其實已經做了一些介紹了，但是看了之后還是不能對完整的流程有個大致的印象，并且其中肯定還是有很多東西值得我們去深挖學習的。

JSPatch簡介

JSPatch 是一個 iOS 動態更新框架，只需在項目中引入極小的引擎，就可以使用 JavaScript 調用任何 Objective-C 原生接口，獲得腳本語言的優勢：為項目動態添加模塊，或替換項目原生代碼動態修復 bug。

大致需要了解的

• JavaScript - 還是要稍微會一點點js的，我就是那種菜的摳腳的水平，所以js部分看的有點吃力。不懂的地方都是靠調試js代碼打斷點，根據結果反向推來搞懂的。
• JSPatch里JavaScript的寫法。還是那句話，用過之后會有一些問題，帶著問題去讀源碼更有針對性，效果更好。
• JavaScriptCore - js和oc內部交互用的是JavaScriptCore，推薦閱讀JavaScriptCore 整體介紹。
• Runtime - JSPatch內部是通過Runtime來動態修改添加方法的，涉及到了很多很多的runtime的知識。所以你還是需要了解一些runtime的知識。推薦閱讀Objective-C Runtime。

帶著問題看源碼

國際慣例，拋磚引玉提倆問題。

1. 添加方法的時候，方法的編碼是怎么做處理的

class_addMethod(Class _Nullable cls, SEL _Nonnull name, IMP _Nonnull imp, const char * _Nullable types) 復制代碼

我知道runtime里添加一個方法里會需要我們傳遞一個方法的編碼。蘋果的運行時庫內部利用類型編碼幫助加快消息分發。方法的編碼主要描述了方法的返回值和參數。比如這樣一個方法-(void)test:(id)arg;最后拿到的編碼是v@:@,具體各個字符對應關系Type Encodings。但是你可能會有個問題這里算上返回值一共就倆個參數，但是這里一共有四個字符。原因是[receiver test:arg]會被編譯器轉化成objc_msgSend(receiver, selector, arg1) 我們拿到的簽名里的參數部分被加上了一個self和一個SEL。

JS里的方法顯然是沒有這樣的編碼的，那么從JS到OC方法的編碼是如何處理的呢。

2. JS function內是怎么調用OC方法的

如果某個JS對象不存在某個方法那么調用是要出錯的。例如UIView.alloc()如果UIView對象沒有alloc這個方法調用是會出問題的。

粗略的看一下流程

簡化了很多細節，demo里的代碼的大致的流程如下。用兩種顏色區分了js端和native端。

從這個流程圖當中我們大致可以了解到，JSPatch最后的方法調用和Aspects庫類似都是走的消息轉發。而且native方法不存在的時候JSPatch并不會去動態生成一個方法。所以當Aspects和JSPatch混用的時候需要特別小心。

回頭看疑問

問題1

關于第一個方法編碼的問題，JSPatch分了幾種情況去處理

• 協議里的方法
• native已經實現了的方法
• 默認的情況

對應的大致的代碼邏輯，可以看到如果是添加了一個之前完全不存在的方法，是需要知道有多少個參數來自己創建一個方法編碼的。所以之前的js里有一步是要生成一個[方法參數個數，方法實現]這樣的數據結構。

// 如果已經實現了這個方法 if (class_respondsToSelector(currCls, NSSelectorFromString(selectorName))) {// overrideMethod方法內部通過下面的邏輯來獲取編碼// Method method = class_getInstanceMethod(cls, selector);// typeDescription = (char *)method_getTypeEncoding(method);overrideMethod(currCls, selectorName, jsMethod, !isInstance, NULL);} else {// 協議方法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;}}// 默認的情況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]);}}} 復制代碼

問題2

關于這個問題bang哥已經有一些介紹，通過正則，類似UIView.alloc().init()的調用被替換成UIView.__c('alloc')().__c('init')()形式。走統一的__c()元函數,傳遞進方法名拿到一個方法，再傳遞進參數調用方法。

實現細節

JSPatch細節有點多。我這邊只挑一些主要的看，默認你已經大致看過源碼。

從demo的執行入口開始

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

startEngine相當于初始化運行環境,它的內部通過JavaScriptCore定義了很多JS的方法，給外部的js來和native交互。

+ (void)startEngine { . . .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);};context[@"_OC_callI"] = ^id(JSValue *obj, NSString *selectorName, JSValue *arguments, BOOL isSuper) {return callSelector(nil, selectorName, arguments, obj, isSuper);};context[@"_OC_callC"] = ^id(NSString *className, NSString *selectorName, JSValue *arguments) {return callSelector(className, selectorName, arguments, nil, NO);};context[@"_OC_formatJSToOC"] = ^id(JSValue *obj) {return formatJSToOC(obj);};context[@"_OC_formatOCToJS"] = ^id(JSValue *obj) {return formatOCToJS([obj toObject]);};... 復制代碼

js可以直接調用這些方法并且傳遞參數，傳遞的參數在這里會自動轉換。具體的轉換對應關系。

Objective-C type | JavaScript type--------------------+---------------------nil | undefinedNSNull | nullNSString | stringNSNumber | number, booleanNSDictionary | Object objectNSArray | Array objectNSDate | Date objectNSBlock (1) | Function object (1)id (2) | Wrapper object (2)Class (3) | Constructor object (3) 復制代碼

上面是環境的初始化，初始化完就是js腳本的調用。[JPEngine evaluateScript:script]; evaluateScript方法的主要作用就是把原始的js方法里方法調用正則修改成__c函數調用。也就是上面問題2的描述。

+ (JSValue *)_evaluateScript:(NSString *)script withSourceURL:(NSURL *)resourceURL {if (!script || ![JSContext class]) {_exceptionBlock(@"script is nil");return nil;}[self startEngine];if (!_regex) {_regex = [NSRegularExpression regularExpressionWithPattern:_regexStr options:0 error:nil];}NSString *formatedScript = [NSString stringWithFormat:@";(function(){try{\n%@\n}catch(e){_OC_catch(e.message, e.stack)}})();", [_regex stringByReplacingMatchesInString:script options:0 range:NSMakeRange(0, script.length) withTemplate:_replaceStr]];@try {if ([_context respondsToSelector:@selector(evaluateScript:withSourceURL:)]) {return [_context evaluateScript:formatedScript withSourceURL:resourceURL];} else {return [_context evaluateScript:formatedScript];}}@catch (NSException *exception) {_exceptionBlock([NSString stringWithFormat:@"%@", exception]);}return nil; } 復制代碼

接下來就是JavaScriptCore執行js腳本了。

defineClass('JPViewController', {viewDidAppear:function(animate) {console.log('lol');},handleBtn: function(sender) {var tableViewCtrl = JPTableViewController.alloc().init()self.navigationController().pushViewController_animated(tableViewCtrl, YES)} }) 復制代碼global.defineClass = function(declaration, properties, instMethods, clsMethods) {var newInstMethods = {}, newClsMethods = {}if (!(properties instanceof Array)) {clsMethods = instMethodsinstMethods = propertiesproperties = null}// 如果有屬性的情況下，需要去判斷有沒有實現set get方法，如果實現了就要加到實例方法列表里面去if (properties) {properties.forEach(function(name){if (!instMethods[name]) {instMethods[name] = _propertiesGetFun(name);}var nameOfSet = "set"+ name.substr(0,1).toUpperCase() + name.substr(1);if (!instMethods[nameOfSet]) {instMethods[nameOfSet] = _propertiesSetFun(name);}});}// 解析出類名var realClsName = declaration.split(':')[0].trim()_formatDefineMethods(instMethods, newInstMethods, realClsName)_formatDefineMethods(clsMethods, newClsMethods, realClsName)var ret = _OC_defineClass(declaration, newInstMethods, newClsMethods)var className = ret['cls']var superCls = ret['superCls']_ocCls[className] = {instMethods: {},clsMethods: {},}if (superCls.length && _ocCls[superCls]) {for (var funcName in _ocCls[superCls]['instMethods']) {_ocCls[className]['instMethods'][funcName] = _ocCls[superCls]['instMethods'][funcName]}for (var funcName in _ocCls[superCls]['clsMethods']) {_ocCls[className]['clsMethods'][funcName] = _ocCls[superCls]['clsMethods'][funcName]}}_setupJSMethod(className, instMethods, 1, realClsName)_setupJSMethod(className, clsMethods, 0, realClsName)return require(className)} 復制代碼

我們看到defineClass方法內部做了一些解析處理，并且調用了我們之前注冊的_OC_defineClass方法，傳遞進去了類名、實例方法、類方法。OC部分的defineClass方法如下

static NSDictionary *defineClass(NSString *classDeclaration, JSValue *instanceMethods, JSValue *classMethods) {NSScanner *scanner = [NSScanner scannerWithString:classDeclaration];NSString *className;NSString *superClassName;NSString *protocolNames;// xxObject : xxSuperObject <xxProtocol>// 解析類[scanner scanUpToString:@":" intoString:&className];if (!scanner.isAtEnd) {// 解析父類scanner.scanLocation = scanner.scanLocation + 1;[scanner scanUpToString:@"<" intoString:&superClassName];// 解析協議if (!scanner.isAtEnd) {scanner.scanLocation = scanner.scanLocation + 1;[scanner scanUpToString:@">" intoString:&protocolNames];}}// 沒有父類信息的情況就繼承自NSObjectif (!superClassName) superClassName = @"NSObject";// 刪除前后空格className = trim(className);superClassName = trim(superClassName);// 解析出協議NSArray *protocols = [protocolNames length] ? [protocolNames componentsSeparatedByString:@","] : nil;Class cls = NSClassFromString(className);if (!cls) {// 如果當前的類不存在Class superCls = NSClassFromString(superClassName);if (!superCls) {// 如果父類不存在直接奔潰_exceptionBlock([NSString stringWithFormat:@"can't find the super class %@", superClassName]);return @{@"cls": className};}// 創建這個類cls = objc_allocateClassPair(superCls, className.UTF8String, 0);objc_registerClassPair(cls);}// 給這個類添加協議if (protocols.count > 0) {for (NSString* protocolName in protocols) {Protocol *protocol = objc_getProtocol([trim(protocolName) cStringUsingEncoding:NSUTF8StringEncoding]);class_addProtocol (cls, protocol);}}// 實例方法和類方法處理 1是實例方法 2是類方法for (int i = 0; i < 2; i ++) {BOOL isInstance = i == 0;// 傳遞過來的方法都是 `方法名` : `[方法參數個數，方法實現]` 這樣的形式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];// 參數的個數int numberOfArg = [jsMethodArr[0] toInt32];// JS的方法名字轉換成OC的方法名字NSString *selectorName = convertJPSelectorString(jsMethodName);// 為了js端的寫法好看點，末尾的參數可以不用寫 `_`if ([selectorName componentsSeparatedByString:@":"].count - 1 < numberOfArg) {selectorName = [selectorName stringByAppendingString:@":"];}JSValue *jsMethod = jsMethodArr[1];// 如果已經實現了這個方法if (class_respondsToSelector(currCls, NSSelectorFromString(selectorName))) {// overrideMethod方法內部通過下面的邏輯來獲取編碼// Method method = class_getInstanceMethod(cls, selector);// typeDescription = (char *)method_getTypeEncoding(method);overrideMethod(currCls, selectorName, jsMethod, !isInstance, NULL);} else {// 協議方法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;}}// 默認的情況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]);}}}}}class_addMethod(cls, @selector(getProp:), (IMP)getPropIMP, "@@:@");class_addMethod(cls, @selector(setProp:forKey:), (IMP)setPropIMP, "v@:@@");return @{@"cls": className, @"superCls": superClassName}; } 復制代碼

我們主要來看一下針對方法部分的操作，可以看到區分不同的情況拿到方法的編碼之后走的都是overrideMethod方法。再來看看這個方法的主要邏輯。

static void overrideMethod(Class cls, NSString *selectorName, JSValue *function, BOOL isClassMethod, const char *typeDescription) {SEL selector = NSSelectorFromString(selectorName);// 拿到方法簽名if (!typeDescription) {Method method = class_getInstanceMethod(cls, selector);typeDescription = (char *)method_getTypeEncoding(method);}// 拿到原始方法的IMP如果方法實現了的話IMP originalImp = class_respondsToSelector(cls, selector) ? class_getMethodImplementation(cls, selector) : NULL;// 拿到消息轉發指針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// 替換消息轉發 `forwardInvocation:`的實現if (class_getMethodImplementation(cls, @selector(forwardInvocation:)) != (IMP)JPForwardInvocation) {IMP originalForwardImp = class_replaceMethod(cls, @selector(forwardInvocation:), (IMP)JPForwardInvocation, "v@:@");if (originalForwardImp) {class_addMethod(cls, @selector(ORIGforwardInvocation:), originalForwardImp, "v@:@");// 存一下原始的IMP}}// invocation return 0 when the return type is double/float.[cls jp_fixMethodSignature];// 如果實現了這個方法，做一下區分生成一個新的 ORIGSelector -> 原始方法的IMP。 為了JS能調用到之前的方法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];_initJPOverideMethods(cls);_JSOverideMethods[cls][JPSelectorName] = function;// Replace the original selector at last, preventing threading issus when// the selector get called during the execution of `overrideMethod`// 調用方法的時候直接走消息轉發class_replaceMethod(cls, selector, msgForwardIMP, typeDescription); } 復制代碼

這個方法和Aspects里的核心方法很像。主要的操作就是替換forwardInvocation的實現，替換要調用的方法的SEL指向_objc_msgForward。也就是方法調用的時候直接走消息轉發，執行JPForwardInvocation方法。并且也把傳遞過來的JS方法存了一下，以便在JPForwardInvocation方法里調用。JPForwardInvocation的方法實在是有點長，它主要的流程如下圖

代碼如下，有刪除一些內容。

static void JPForwardInvocation(__unsafe_unretained id assignSlf, SEL selector, NSInvocation *invocation) {// 調用棧 #ifdef DEBUG_JSLastCallStack = [NSThread callStackSymbols]; #endifBOOL deallocFlag = NO;id slf = assignSlf;// 方法簽名NSMethodSignature *methodSignature = [invocation methodSignature];// 方法參數NSInteger numberOfArguments = [methodSignature numberOfArguments];// 方法名字NSString *selectorName = NSStringFromSelector(invocation.selector);// JS方法名字NSString *JPSelectorName = [NSString stringWithFormat:@"_JP%@", selectorName];// 拿到js的functionJSValue *jsFunc = getJSFunctionInObjectHierachy(slf, JPSelectorName);if (!jsFunc) {// 如果沒有實現JS的方法就調用原始的消息轉發JPExecuteORIGForwardInvocation(slf, selector, invocation);return;}// JPBoxing的作用是防止強制轉換NSMutableArray *argList = [[NSMutableArray alloc] init];if ([slf class] == slf) {// 類方法[argList addObject:[JSValue valueWithObject:@{@"__clsName": NSStringFromClass([slf class])} inContext:_context]];} else if ([selectorName isEqualToString:@"dealloc"]) {// dealloc方法添加一個assign的self對象[argList addObject:[JPBoxing boxAssignObj:slf]];deallocFlag = YES;} else {// 默認的情況添加一個weak的self對象[argList addObject:[JPBoxing boxWeakObj:slf]];}// 方法簽名的 0是self 1是_cmd// 遍歷獲取方法的參數,for (NSUInteger i = 2; i < numberOfArguments; i++) {const char *argumentType = [methodSignature getArgumentTypeAtIndex:i];switch(argumentType[0] == 'r' ? argumentType[1] : argumentType[0]) {// 基礎數據類型#define JP_FWD_ARG_CASE(_typeChar, _type) \case _typeChar: { \_type arg; \[invocation getArgument:&arg atIndex:i]; \[argList addObject:@(arg)]; \break; \}JP_FWD_ARG_CASE('c', char)JP_FWD_ARG_CASE('C', unsigned char)JP_FWD_ARG_CASE('s', short)JP_FWD_ARG_CASE('S', unsigned short)JP_FWD_ARG_CASE('i', int)JP_FWD_ARG_CASE('I', unsigned int)JP_FWD_ARG_CASE('l', long)JP_FWD_ARG_CASE('L', unsigned long)JP_FWD_ARG_CASE('q', long long)JP_FWD_ARG_CASE('Q', unsigned long long)JP_FWD_ARG_CASE('f', float)JP_FWD_ARG_CASE('d', double)JP_FWD_ARG_CASE('B', BOOL)// 對象case '@': {__unsafe_unretained id arg;[invocation getArgument:&arg atIndex:i];if ([arg isKindOfClass:NSClassFromString(@"NSBlock")]) {[argList addObject:(arg ? [arg copy]: _nilObj)];} else {[argList addObject:(arg ? arg: _nilObj)];}break;}// structcase '{': {NSString *typeString = extractStructName([NSString stringWithUTF8String:argumentType]);#define JP_FWD_ARG_STRUCT(_type, _transFunc) \if ([typeString rangeOfString:@#_type].location != NSNotFound) { \_type arg; \[invocation getArgument:&arg atIndex:i]; \[argList addObject:[JSValue _transFunc:arg inContext:_context]]; \break; \}JP_FWD_ARG_STRUCT(CGRect, valueWithRect)JP_FWD_ARG_STRUCT(CGPoint, valueWithPoint)JP_FWD_ARG_STRUCT(CGSize, valueWithSize)JP_FWD_ARG_STRUCT(NSRange, valueWithRange)@synchronized (_context) {NSDictionary *structDefine = _registeredStruct[typeString];if (structDefine) {size_t size = sizeOfStructTypes(structDefine[@"types"]);if (size) {void *ret = malloc(size);[invocation getArgument:ret atIndex:i];NSDictionary *dict = getDictOfStruct(ret, structDefine);[argList addObject:[JSValue valueWithObject:dict inContext:_context]];free(ret);break;}}}break;}case ':': {SEL selector;[invocation getArgument:&selector atIndex:i];NSString *selectorName = NSStringFromSelector(selector);[argList addObject:(selectorName ? selectorName: _nilObj)];break;}// 指針case '^':case '*': {void *arg;[invocation getArgument:&arg atIndex:i];[argList addObject:[JPBoxing boxPointer:arg]];break;}// 類case '#': {Class arg;[invocation getArgument:&arg atIndex:i];[argList addObject:[JPBoxing boxClass:arg]];break;}default: {NSLog(@"error type %s", argumentType);break;}}}// 調用父類方法if (_currInvokeSuperClsName[selectorName]) {Class cls = NSClassFromString(_currInvokeSuperClsName[selectorName]);NSString *tmpSelectorName = [[selectorName stringByReplacingOccurrencesOfString:@"_JPSUPER_" withString:@"_JP"] stringByReplacingOccurrencesOfString:@"SUPER_" withString:@"_JP"];if (!_JSOverideMethods[cls][tmpSelectorName]) {NSString *ORIGSelectorName = [selectorName stringByReplacingOccurrencesOfString:@"SUPER_" withString:@"ORIG"];[argList removeObjectAtIndex:0];id retObj = callSelector(_currInvokeSuperClsName[selectorName], ORIGSelectorName, [JSValue valueWithObject:argList inContext:_context], [JSValue valueWithObject:@{@"__obj": slf, @"__realClsName": @""} inContext:_context], NO);id __autoreleasing ret = formatJSToOC([JSValue valueWithObject:retObj inContext:_context]);[invocation setReturnValue:&ret];return;}}// 把oc的參數轉成js的參數NSArray *params = _formatOCToJSList(argList);// 返回數據的encodechar returnType[255];strcpy(returnType, [methodSignature methodReturnType]);// 處理7.1系統下返回double float 0的問題// Restore the return typeif (strcmp(returnType, @encode(JPDouble)) == 0) {strcpy(returnType, @encode(double));}if (strcmp(returnType, @encode(JPFloat)) == 0) {strcpy(returnType, @encode(float));}// 拿到jsFunc 直接調用 `[jsFunc callWithArguments:params]` 然后根據returnType轉成對應的OC數據switch (returnType[0] == 'r' ? returnType[1] : returnType[0]) {#define JP_FWD_RET_CALL_JS \JSValue *jsval; \[_JSMethodForwardCallLock lock]; \jsval = [jsFunc callWithArguments:params]; \[_JSMethodForwardCallLock unlock]; \while (![jsval isNull] && ![jsval isUndefined] && [jsval hasProperty:@"__isPerformInOC"]) { \NSArray *args = nil; \JSValue *cb = jsval[@"cb"]; \if ([jsval hasProperty:@"sel"]) { \id callRet = callSelector(![jsval[@"clsName"] isUndefined] ? [jsval[@"clsName"] toString] : nil, [jsval[@"sel"] toString], jsval[@"args"], ![jsval[@"obj"] isUndefined] ? jsval[@"obj"] : nil, NO); \args = @[[_context[@"_formatOCToJS"] callWithArguments:callRet ? @[callRet] : _formatOCToJSList(@[_nilObj])]]; \} \[_JSMethodForwardCallLock lock]; \jsval = [cb callWithArguments:args]; \[_JSMethodForwardCallLock unlock]; \}#define JP_FWD_RET_CASE_RET(_typeChar, _type, _retCode) \case _typeChar : { \JP_FWD_RET_CALL_JS \_retCode \[invocation setReturnValue:&ret];\break; \}#define JP_FWD_RET_CASE(_typeChar, _type, _typeSelector) \JP_FWD_RET_CASE_RET(_typeChar, _type, _type ret = [[jsval toObject] _typeSelector];) \#define JP_FWD_RET_CODE_ID \id __autoreleasing ret = formatJSToOC(jsval); \if (ret == _nilObj || \([ret isKindOfClass:[NSNumber class]] && strcmp([ret objCType], "c") == 0 && ![ret boolValue])) ret = nil; \#define JP_FWD_RET_CODE_POINTER \void *ret; \id obj = formatJSToOC(jsval); \if ([obj isKindOfClass:[JPBoxing class]]) { \ret = [((JPBoxing *)obj) unboxPointer]; \}#define JP_FWD_RET_CODE_CLASS \Class ret; \ret = formatJSToOC(jsval);#define JP_FWD_RET_CODE_SEL \SEL ret; \id obj = formatJSToOC(jsval); \if ([obj isKindOfClass:[NSString class]]) { \ret = NSSelectorFromString(obj); \}JP_FWD_RET_CASE_RET('@', id, JP_FWD_RET_CODE_ID)JP_FWD_RET_CASE_RET('^', void*, JP_FWD_RET_CODE_POINTER)JP_FWD_RET_CASE_RET('*', void*, JP_FWD_RET_CODE_POINTER)JP_FWD_RET_CASE_RET('#', Class, JP_FWD_RET_CODE_CLASS)JP_FWD_RET_CASE_RET(':', SEL, JP_FWD_RET_CODE_SEL)JP_FWD_RET_CASE('c', char, charValue)JP_FWD_RET_CASE('C', unsigned char, unsignedCharValue)JP_FWD_RET_CASE('s', short, shortValue)JP_FWD_RET_CASE('S', unsigned short, unsignedShortValue)JP_FWD_RET_CASE('i', int, intValue)JP_FWD_RET_CASE('I', unsigned int, unsignedIntValue)JP_FWD_RET_CASE('l', long, longValue)JP_FWD_RET_CASE('L', unsigned long, unsignedLongValue)JP_FWD_RET_CASE('q', long long, longLongValue)JP_FWD_RET_CASE('Q', unsigned long long, unsignedLongLongValue)JP_FWD_RET_CASE('f', float, floatValue)JP_FWD_RET_CASE('d', double, doubleValue)JP_FWD_RET_CASE('B', BOOL, boolValue)case 'v': {JP_FWD_RET_CALL_JSbreak;}case '{': {NSString *typeString = extractStructName([NSString stringWithUTF8String:returnType]);#define JP_FWD_RET_STRUCT(_type, _funcSuffix) \if ([typeString rangeOfString:@#_type].location != NSNotFound) { \JP_FWD_RET_CALL_JS \_type ret = [jsval _funcSuffix]; \[invocation setReturnValue:&ret];\break; \}JP_FWD_RET_STRUCT(CGRect, toRect)JP_FWD_RET_STRUCT(CGPoint, toPoint)JP_FWD_RET_STRUCT(CGSize, toSize)JP_FWD_RET_STRUCT(NSRange, toRange)@synchronized (_context) {NSDictionary *structDefine = _registeredStruct[typeString];if (structDefine) {size_t size = sizeOfStructTypes(structDefine[@"types"]);JP_FWD_RET_CALL_JSvoid *ret = malloc(size);NSDictionary *dict = formatJSToOC(jsval);getStructDataWithDict(ret, dict, structDefine);[invocation setReturnValue:ret];free(ret);}}break;}default: {break;}}... } 復制代碼

上面的流程主要是定義一個js的方法然后進行的一些操作。

下面再來看一下js方法內部是如何調用原生的方法的。JS部分的代碼就不貼全了，主要的操作邏輯是給JS 對象基類對象加加上__c成員，這樣所有對象都可以調用到__c, __c內部還有一些判斷是否是對象、是否調用的是父類的方法等等的操作，最后調用的是_methodFunc方法。

var _methodFunc = function(instance, clsName, methodName, args, isSuper, isPerformSelector) {var selectorName = methodNameif (!isPerformSelector) {methodName = methodName.replace(/__/g, "-")selectorName = methodName.replace(/_/g, ":").replace(/-/g, "_")var marchArr = selectorName.match(/:/g)var numOfArgs = marchArr ? marchArr.length : 0if (args.length > numOfArgs) {selectorName += ":"}}var ret = instance ? _OC_callI(instance, selectorName, args, isSuper):_OC_callC(clsName, selectorName, args)return _formatOCToJS(ret)} 復制代碼

然后我們看到，方法內部做了一些判斷和解析。最后對象方法調用的是在native里注冊了的_OC_callI類方法調用的是在native里注冊了的_OC_callC方法。這兩個方法都走的是callSelector方法。這個方法也是老長。它的主要流程圖如下。

代碼如下

static id callSelector(NSString *className, NSString *selectorName, JSValue *arguments, JSValue *instance, BOOL isSuper) {NSString *realClsName = [[instance valueForProperty:@"__realClsName"] toString];if (instance) {// JSValue -> OC對象instance = formatJSToOC(instance);if (class_isMetaClass(object_getClass(instance))) {// 是否是類對象className = NSStringFromClass((Class)instance);instance = nil;} else if (!instance || instance == _nilObj || [instance isKindOfClass:[JPBoxing class]]) { // 空對象return @{@"__isNil": @(YES)};}}// 參數id argumentsObj = formatJSToOC(arguments);if (instance && [selectorName isEqualToString:@"toJS"]) {if ([instance isKindOfClass:[NSString class]] || [instance isKindOfClass:[NSDictionary class]] || [instance isKindOfClass:[NSArray class]] || [instance isKindOfClass:[NSDate class]]) {return _unboxOCObjectToJS(instance);}}// 類Class cls = instance ? [instance class] : NSClassFromString(className);SEL selector = NSSelectorFromString(selectorName);// 父類NSString *superClassName = nil;if (isSuper) {NSString *superSelectorName = [NSString stringWithFormat:@"SUPER_%@", selectorName];SEL superSelector = NSSelectorFromString(superSelectorName);Class superCls;if (realClsName.length) {Class defineClass = NSClassFromString(realClsName);superCls = defineClass ? [defineClass superclass] : [cls superclass];} else {superCls = [cls superclass];}Method superMethod = class_getInstanceMethod(superCls, selector);IMP superIMP = method_getImplementation(superMethod);class_addMethod(cls, superSelector, superIMP, method_getTypeEncoding(superMethod));NSString *JPSelectorName = [NSString stringWithFormat:@"_JP%@", selectorName];JSValue *overideFunction = _JSOverideMethods[superCls][JPSelectorName];if (overideFunction) {overrideMethod(cls, superSelectorName, overideFunction, NO, NULL);}selector = superSelector;superClassName = NSStringFromClass(superCls);}NSMutableArray *_markArray;// 方法編碼NSInvocation *invocation;NSMethodSignature *methodSignature;if (!_JSMethodSignatureCache) {_JSMethodSignatureCache = [[NSMutableDictionary alloc]init];}if (instance) {[_JSMethodSignatureLock lock];if (!_JSMethodSignatureCache[cls]) {_JSMethodSignatureCache[(id<NSCopying>)cls] = [[NSMutableDictionary alloc]init];}methodSignature = _JSMethodSignatureCache[cls][selectorName];if (!methodSignature) {methodSignature = [cls instanceMethodSignatureForSelector:selector];methodSignature = fixSignature(methodSignature);_JSMethodSignatureCache[cls][selectorName] = methodSignature;}[_JSMethodSignatureLock unlock];if (!methodSignature) {_exceptionBlock([NSString stringWithFormat:@"unrecognized selector %@ for instance %@", selectorName, instance]);return nil;}invocation = [NSInvocation invocationWithMethodSignature:methodSignature];[invocation setTarget:instance];} else {methodSignature = [cls methodSignatureForSelector:selector];methodSignature = fixSignature(methodSignature);if (!methodSignature) {_exceptionBlock([NSString stringWithFormat:@"unrecognized selector %@ for class %@", selectorName, className]);return nil;}invocation= [NSInvocation invocationWithMethodSignature:methodSignature];[invocation setTarget:cls];}[invocation setSelector:selector];NSUInteger numberOfArguments = methodSignature.numberOfArguments;NSInteger inputArguments = [(NSArray *)argumentsObj count];if (inputArguments > numberOfArguments - 2) {// calling variable argument method, only support parameter type `id` and return type `id`id sender = instance != nil ? instance : cls;id result = invokeVariableParameterMethod(argumentsObj, methodSignature, sender, selector);return formatOCToJS(result);}// 設置方法參數for (NSUInteger i = 2; i < numberOfArguments; i++) {const char *argumentType = [methodSignature getArgumentTypeAtIndex:i];id valObj = argumentsObj[i-2];switch (argumentType[0] == 'r' ? argumentType[1] : argumentType[0]) {#define JP_CALL_ARG_CASE(_typeString, _type, _selector) \case _typeString: { \_type value = [valObj _selector]; \[invocation setArgument:&value atIndex:i];\break; \}JP_CALL_ARG_CASE('c', char, charValue)JP_CALL_ARG_CASE('C', unsigned char, unsignedCharValue)JP_CALL_ARG_CASE('s', short, shortValue)JP_CALL_ARG_CASE('S', unsigned short, unsignedShortValue)JP_CALL_ARG_CASE('i', int, intValue)JP_CALL_ARG_CASE('I', unsigned int, unsignedIntValue)JP_CALL_ARG_CASE('l', long, longValue)JP_CALL_ARG_CASE('L', unsigned long, unsignedLongValue)JP_CALL_ARG_CASE('q', long long, longLongValue)JP_CALL_ARG_CASE('Q', unsigned long long, unsignedLongLongValue)JP_CALL_ARG_CASE('f', float, floatValue)JP_CALL_ARG_CASE('d', double, doubleValue)JP_CALL_ARG_CASE('B', BOOL, boolValue)case ':': {SEL value = nil;if (valObj != _nilObj) {value = NSSelectorFromString(valObj);}[invocation setArgument:&value atIndex:i];break;}case '{': {NSString *typeString = extractStructName([NSString stringWithUTF8String:argumentType]);JSValue *val = arguments[i-2];#define JP_CALL_ARG_STRUCT(_type, _methodName) \if ([typeString rangeOfString:@#_type].location != NSNotFound) { \_type value = [val _methodName]; \[invocation setArgument:&value atIndex:i]; \break; \}JP_CALL_ARG_STRUCT(CGRect, toRect)JP_CALL_ARG_STRUCT(CGPoint, toPoint)JP_CALL_ARG_STRUCT(CGSize, toSize)JP_CALL_ARG_STRUCT(NSRange, toRange)@synchronized (_context) {NSDictionary *structDefine = _registeredStruct[typeString];if (structDefine) {size_t size = sizeOfStructTypes(structDefine[@"types"]);void *ret = malloc(size);getStructDataWithDict(ret, valObj, structDefine);[invocation setArgument:ret atIndex:i];free(ret);break;}}break;}case '*':case '^': {if ([valObj isKindOfClass:[JPBoxing class]]) {void *value = [((JPBoxing *)valObj) unboxPointer];if (argumentType[1] == '@') {if (!_TMPMemoryPool) {_TMPMemoryPool = [[NSMutableDictionary alloc] init];}if (!_markArray) {_markArray = [[NSMutableArray alloc] init];}memset(value, 0, sizeof(id));[_markArray addObject:valObj];}[invocation setArgument:&value atIndex:i];break;}}case '#': {if ([valObj isKindOfClass:[JPBoxing class]]) {Class value = [((JPBoxing *)valObj) unboxClass];[invocation setArgument:&value atIndex:i];break;}}default: {if (valObj == _nullObj) {valObj = [NSNull null];[invocation setArgument:&valObj atIndex:i];break;}if (valObj == _nilObj ||([valObj isKindOfClass:[NSNumber class]] && strcmp([valObj objCType], "c") == 0 && ![valObj boolValue])) {valObj = nil;[invocation setArgument:&valObj atIndex:i];break;}if ([(JSValue *)arguments[i-2] hasProperty:@"__isBlock"]) {JSValue *blkJSVal = arguments[i-2];Class JPBlockClass = NSClassFromString(@"JPBlock");if (JPBlockClass && ![blkJSVal[@"blockObj"] isUndefined]) {__autoreleasing id cb = [JPBlockClass performSelector:@selector(blockWithBlockObj:) withObject:[blkJSVal[@"blockObj"] toObject]];[invocation setArgument:&cb atIndex:i];Block_release((__bridge void *)cb);} else {__autoreleasing id cb = genCallbackBlock(arguments[i-2]);[invocation setArgument:&cb atIndex:i];}} else {[invocation setArgument:&valObj atIndex:i];}}}}if (superClassName) _currInvokeSuperClsName[selectorName] = superClassName;[invocation invoke];if (superClassName) [_currInvokeSuperClsName removeObjectForKey:selectorName];if ([_markArray count] > 0) {for (JPBoxing *box in _markArray) {void *pointer = [box unboxPointer];id obj = *((__unsafe_unretained id *)pointer);if (obj) {@synchronized(_TMPMemoryPool) {[_TMPMemoryPool setObject:obj forKey:[NSNumber numberWithInteger:[(NSObject*)obj hash]]];}}}}char returnType[255];strcpy(returnType, [methodSignature methodReturnType]);// Restore the return typeif (strcmp(returnType, @encode(JPDouble)) == 0) {strcpy(returnType, @encode(double));}if (strcmp(returnType, @encode(JPFloat)) == 0) {strcpy(returnType, @encode(float));}// 方法返回值處理id returnValue;if (strncmp(returnType, "v", 1) != 0) {if (strncmp(returnType, "@", 1) == 0) {void *result;[invocation getReturnValue:&result];//For performance, ignore the other methods prefix with alloc/new/copy/mutableCopyif ([selectorName isEqualToString:@"alloc"] || [selectorName isEqualToString:@"new"] ||[selectorName isEqualToString:@"copy"] || [selectorName isEqualToString:@"mutableCopy"]) {returnValue = (__bridge_transfer id)result;} else {returnValue = (__bridge id)result;}return formatOCToJS(returnValue);} else {switch (returnType[0] == 'r' ? returnType[1] : returnType[0]) {#define JP_CALL_RET_CASE(_typeString, _type) \case _typeString: { \_type tempResultSet; \[invocation getReturnValue:&tempResultSet];\returnValue = @(tempResultSet); \break; \}JP_CALL_RET_CASE('c', char)JP_CALL_RET_CASE('C', unsigned char)JP_CALL_RET_CASE('s', short)JP_CALL_RET_CASE('S', unsigned short)JP_CALL_RET_CASE('i', int)JP_CALL_RET_CASE('I', unsigned int)JP_CALL_RET_CASE('l', long)JP_CALL_RET_CASE('L', unsigned long)JP_CALL_RET_CASE('q', long long)JP_CALL_RET_CASE('Q', unsigned long long)JP_CALL_RET_CASE('f', float)JP_CALL_RET_CASE('d', double)JP_CALL_RET_CASE('B', BOOL)case '{': {NSString *typeString = extractStructName([NSString stringWithUTF8String:returnType]);#define JP_CALL_RET_STRUCT(_type, _methodName) \if ([typeString rangeOfString:@#_type].location != NSNotFound) { \_type result; \[invocation getReturnValue:&result]; \return [JSValue _methodName:result inContext:_context]; \}JP_CALL_RET_STRUCT(CGRect, valueWithRect)JP_CALL_RET_STRUCT(CGPoint, valueWithPoint)JP_CALL_RET_STRUCT(CGSize, valueWithSize)JP_CALL_RET_STRUCT(NSRange, valueWithRange)@synchronized (_context) {NSDictionary *structDefine = _registeredStruct[typeString];if (structDefine) {size_t size = sizeOfStructTypes(structDefine[@"types"]);void *ret = malloc(size);[invocation getReturnValue:ret];NSDictionary *dict = getDictOfStruct(ret, structDefine);free(ret);return dict;}}break;}case '*':case '^': {void *result;[invocation getReturnValue:&result];returnValue = formatOCToJS([JPBoxing boxPointer:result]);if (strncmp(returnType, "^{CG", 4) == 0) {if (!_pointersToRelease) {_pointersToRelease = [[NSMutableArray alloc] init];}[_pointersToRelease addObject:[NSValue valueWithPointer:result]];CFRetain(result);}break;}case '#': {Class result;[invocation getReturnValue:&result];returnValue = formatOCToJS([JPBoxing boxClass:result]);break;}}return returnValue;}}return nil; } 復制代碼

ok,到這里一些基本的流程就已經走完了。你可以大致感受到，其中有很大的一部分代碼是在做類型轉換的工作。這轉換的過程中還有很多的細節，比如可變對象的處理等等這里沒有具體展開來講。有興趣可以研究研究。

總結

• js和native的交互用的是JavaScriptCore。
• 替換添加方法都是直接走的方法交換。不存在的方法不會添加。
• 方法的調用用的都是NSInvocation。
• 參數、返回值的格式都是通過編碼來處理。

最后

看完JSPatch的源碼，加上最近一直在玩JSBox。有些想要自己實現一個簡單的JSBox的沖動，定個小目標，準備最近好好看看JS，然后嘗試嘗試。

水文一篇，希望能幫到大家一點點。

總結

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