Aspects 源代码解析<一>

本文详细介绍了Aspects作为面向切面编程(AOP)在iOS下Objective-C(OC)的实现方式,阐述了其在解决权限判断、日志记录等重复操作问题上的优势。Aspects通过hook函数实现副操作,如打印调试信息或记录日志,降低了逻辑过程中的耦合性,提供了一种高效维护和复用代码的方法。

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Aspects 是什么,解决了什么问题?

Aspects是AOP(面向切面编程)思想在iOS下OC的实现。Aspects可以用于hook函数,让函数执行一些副操作(打印调试信息、记录日志等)。切面可以简单理解为嵌入不同函数中的功能相同的操作(打印调试信息等),每类功能相同的操作可以抽取出一个切面。下面简要介绍OOP(面向对象编程)和AOP的概念和区别:

  • OOP(面向对象编程)针对业务处理过程的实体及其属性和行为进行抽象封装,以获得更加清晰高效的逻辑单元划分。
  • AOP则是针对业务处理过程中的切面进行提取,它所面对的是处理过程中的某个步骤或阶段,以获得逻辑过程中各部分之间低耦合性的隔离效果。

OOP实际上是对对象的属性和行为的封装,而AOP对于这点就无从谈起,但是AOP是处理某个步骤和阶段的,从中进行切面的提取,也就是说,如果几个或更多个逻辑过程中,有重复的操作行为,AOP就可以提取出来,运用动态代理,实现程序功能的统一维护,这么说来可能太含蓄,如果说到权限判断,日志记录等,可能就明白了。如果我们单纯使用OOP,那么权限判断怎么办?在每个操作前都加入权限判断?日志记录怎么办?在每个方法里的开始、结束、异常的地方手动添加日志?所有,如果使用AOP就可以借助代理完成这些重复的操作,就能够在逻辑过程中,降低各部分之间的耦合了。二者扬长补短,互相结合最好。

Aspects的思路及实现

思路

Aspects对外暴露了两个接口,用于hook selector:

#pragma mark - Public Aspects API

+ (id<AspectToken>)aspect_hookSelector:(SEL)selector
                      withOptions:(AspectOptions)options
                       usingBlock:(id)block
                            error:(NSError **)error {
    return aspect_add((id)self, selector, options, block, error);
}

/// @return A token which allows to later deregister the aspect.
- (id<AspectToken>)aspect_hookSelector:(SEL)selector
                      withOptions:(AspectOptions)options
                       usingBlock:(id)block
                            error:(NSError **)error {
    return aspect_add(self, selector, options, block, error);
}

参数说明:

selectoroptionsblockerror
要被hook的selector切面(block)执行的时机,在selector执行前、后执行,还是替换被hook的selector切面hook过程中的错误

方法说明:

  1. 第一个方法为类方法,receiver为要被hook的类([receiver message])。直接在本类上hook类的实例方法(被KVO过的类,直接在KVO过程中生成的子类上进行hook实例方法),进行method swizzling,对类的methodListsstruct objc_method_list **methodLists进行修改,修改的方法有两个:

    1. forwardInvocation:
      forwardInvocation: 的IMP(方法实现)被替换为:__ASPECTS_ARE_BEING_CALLED__,该函数内部具体执行被hook的selector和切入的操作,forwardInvocation: 的本来的IMP被保存在__aspects_forwardInvocation:中。forwardInvocation:的method swizzling操作是在static Class aspect_hookClass(NSObject *self, NSError **error)中进行的;
    2. 被hook的selector。被hook的selector的IMP被替换为:_objc_msgForward/_objc_msgForward_stret,该方法用于触发消息转发,被hook的selector的本来的IMP被保存在aliasSelector中。被hook的selector 的method swizzling 是在static void aspect_prepareClassAndHookSelector(NSObject *self, SEL selector, NSError **error)中进行的。
  2. 第二个方法为实例方法,receiver为要被hook的类的实例。用该方法hook实例方法较复杂,步骤简述如下:

    1. 新生成一个被hook类的子类,
    2. 利用isa swizzle将该实例的isa Class isa指向新生成的被hook类的子类,
    3. 对被hook类的子类进行method swizzling,method swizzling的思路与上面类方法的method swizzling相同。

这里直接拿世健同学的例子来讲解吧:

@interface Target : NSObject
- (void)targetSelector;
@end

- (void)targetSelector
{
    NSLog(@"%@'s original selector: %@", self, NSStringFromSelector(_cmd));
}

我们要对Target类的targetSelector进行hook,以方法二(实例方法)为例进行讲解,假定aTarget为Target类的一个实例方法。

    Target *aTarget = [[Target alloc] init];
    [aTarget aspect_hookSelector:NSSelectorFromString(@"targetSelector")
                     withOptions:AspectPositionBefore
                      usingBlock:^(id<AspectInfo> aspectInfo) {
        NSLog(@"Hook targetSelector");
    }
                           error:NULL];
    [aTarget targetSelector];

hook之前aTarget及targetSelector的指向:
hook之前aTarget及targetSelector的指向

hook的过程:

hook Class(“isa swizzling”):
  1. 通过statedClass = self.class获取self本来的class(class方法被重写了,用来获取self被hook之前的Class(Target)。下文交代class方法是如何被重写的);
  2. 通过Class baseClass = object_getClass(self)获取self的isa指针实际指向的class(self在运行时实际的class,表面上看这是一只皮鞋(statedClass),实际上这是一只刮胡刀(basedClass))。
  3. 如果baseClass(实际指向的class)已经是被hook过的子类,则返回baseClass。
  4. 如果baseClass是MetaClass或者被KVO过的Class,则不必再生成subClass,直接在其自身上进行method swizzling。
  5. 如果不是上述3. 、4. 所述情况,默认情况下需要对被hook的Class进行”isa swizzling”:
    1. 通过subclass = objc_allocateClassPair(baseClass, subclassName, 0)动态创建一个被hook类(Target)的子类(Target_Aspects_);
    2. 然后对子类的forwardInvocation:进行method swizzling,替换为__ASPECTS_ARE_BEING_CALLED__,进行消息转发时,实际执行的是__ASPECTS_ARE_BEING_CALLED__中的方法;
    3. 重写子类的获取类名的方法class,使其返回被hook之前的类的类名;
    4. 将self(aTarget)的isa指针指向子类Target_Aspects_object_setClass(self, subclass))。

class被hook后的情况:
class 被hook完成后

#pragma mark - Hook Class

static Class aspect_hookClass(NSObject *self, NSError **error) {
    NSCParameterAssert(self);
    Class statedClass = self.class;
    Class baseClass = object_getClass(self);
    NSString *className = NSStringFromClass(baseClass);

    // Already subclassed
    if ([className hasSuffix:AspectsSubclassSuffix]) {
        return baseClass;

        // We swizzle a class object, not a single object.
    }else if (class_isMetaClass(baseClass)) {
        return aspect_swizzleClassInPlace((Class)self);
        // Probably a KVO'ed class. Swizzle in place. Also swizzle meta classes in place.
    }else if (statedClass != baseClass) {
        return aspect_swizzleClassInPlace(baseClass);
    }

    // Default case. Create dynamic subclass.
    const char *subclassName = [className stringByAppendingString:AspectsSubclassSuffix].UTF8String;
    Class subclass = objc_getClass(subclassName);

    if (subclass == nil) {
        subclass = objc_allocateClassPair(baseClass, subclassName, 0);
        if (subclass == nil) {
            NSString *errrorDesc = [NSString stringWithFormat:@"objc_allocateClassPair failed to allocate class %s.", subclassName];
            AspectError(AspectErrorFailedToAllocateClassPair, errrorDesc);
            return nil;
        }

        aspect_swizzleForwardInvocation(subclass);
        aspect_hookedGetClass(subclass, statedClass);
        aspect_hookedGetClass(object_getClass(subclass), statedClass);
        objc_registerClassPair(subclass);
    }

    object_setClass(self, subclass);
    return subclass;
}
hook selector:
  1. 用新生成的aspects__targetSelector指向selector的IMP;
  2. 将selector指向_objc_msgForward(或者_objc_msgForward_stret,与前者的区别为返回值的不同,该实现返回结构体?)。

selector 被hook后:

selector 被hook后

经过上面hook class和hook selector,Target的targetSelector就被hook进“切面”了。当调用[aTarget targetSelector]时,程序流程如下:

hook后[aTarget targetSelector]的调用流程

参考:
http://www.cnblogs.com/jyh317/p/3834271.html 简单理解AOP(面向切面编程)
http://blog.ibireme.com/2013/11/26/objective-c-messaging/ Objective-C 中的消息与消息转发
http://blog.cnbang.net/tech/2855/ JSPatch实现原理详解<二>

DESUtil.java:package com.source.root.tools.util; import java.io.IOException; import java.security.SecureRandom; import javax.crypto.Cipher; import javax.crypto.SecretKey; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.DESKeySpec; import java.util.Base64; // import sun.misc.BASE64Decoder; // import sun.misc.BASE64Encoder; public class DESUtil { private final static String DES = "DES/CBC/PKCS5Padding"; private static final Base64.Encoder BASE64_ENCODER = Base64.getEncoder(); private static final Base64.Decoder BASE64_DECODER = Base64.getDecoder(); public static void main(String[] args) throws Exception { String data = "123456789"; String key = "jia%duo$"; System.err.println(encrypt(data, key)); System.err.println(decrypt(encrypt(data, key), key)); } /** * Description 根据键值进行加密 * * @param data * @param key * 加密键byte数组 * @return * @throws Exception */ public static String encrypt(String data, String key) throws Exception { byte[] bt = encrypt(data.getBytes(), key.getBytes()); return BASE64_ENCODER.encodeToString(bt); } /** * Description 根据键值进行解密 * * @param data * @param key * 加密键byte数组 * @return * @throws IOException * @throws Exception */ public static String decrypt(String data, String key) throws IOException, Exception { if (data == null) return null; byte[] buf = BASE64_DECODER.decode(data); byte[] bt = decrypt(buf, key.getBytes()); return new String(bt); } /** * Description 根据键值进行加密 * * @param data * @param key * 加密键byte数组 * @return * @throws Exception */ private static byte[] encrypt(byte[] data, byte[] key) throws Exception { // 生成个可信任的随机数源 SecureRandom sr = new SecureRandom(); // 从原始密钥数据创建DESKeySpec对象 DESKeySpec dks = new DESKeySpec(key); // 创建个密钥工厂,然后用它把DESKeySpec转换成SecretKey对象 SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES"); SecretKey securekey = keyFactory.generateSecret(dks); // Cipher对象实际完成加密操作 Cipher cipher = Cipher.getInstance("DES"); // 用密钥初始化Cipher对象 cipher.init(Cipher.ENCRYPT_MODE, securekey, sr); return cipher.doFinal(data); } /** * Description 根据键值进行解密 * * @param data * @param key * 加密键byte数组 * @return * @throws Exception */ private static byte[] decrypt(byte[] data, byte[] key) throws Exception { // 生成个可信任的随机数源 SecureRandom sr = new SecureRandom(); // 从原始密钥数据创建DESKeySpec对象 DESKeySpec dks = new DESKeySpec(key); // 创建个密钥工厂,然后用它把DESKeySpec转换成SecretKey对象 SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES"); SecretKey securekey = keyFactory.generateSecret(dks); // Cipher对象实际完成解密操作 Cipher cipher = Cipher.getInstance("DES"); // 用密钥初始化Cipher对象 cipher.init(Cipher.DECRYPT_MODE, securekey, sr); return cipher.doFinal(data); } } pom.xml:<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>jdwlw</groupId> <artifactId>jdwlw</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>war</packaging> <name>maven Maven Webapp</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> <!-- <dependency> <groupId>javax.servlet</groupId> <artifactId>javax.servlet-api</artifactId> <version>3.1.0</version> </dependency> --> <dependency> <groupId>javax.servlet</groupId> <artifactId>servlet-api</artifactId> <version>2.5</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-beans</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-aop</artifactId> <version>4.1.6.RELEASE</version> </dependency> <!-- https://mvnrepository.com/artifact/org.ksoap2/ksoap2 --> <!-- <dependency> <groupId>org.ksoap2</groupId> <artifactId>ksoap2</artifactId> <version>2.1.2</version> </dependency> --> <dependency> <groupId>com.google.code.ksoap2-android</groupId> <artifactId>ksoap2-android</artifactId> <version>3.6.4</version> </dependency> <dependency> <groupId>javax.xml.soap</groupId> <artifactId>javax.xml.soap-api</artifactId> <version>1.4.0</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-jdbc</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-web</artifactId> <version>4.1.6.RELEASE</version> </dependency> <!-- <dependency> <groupId>org.springframework</groupId> <artifactId>spring-orm</artifactId> <version>4.1.6.RELEASE</version> </dependency> --> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-orm</artifactId> <version>3.2.13.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context-support</artifactId> <version>3.2.2.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc-portlet</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-expression</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-aspects</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-websocket</artifactId> <version>4.1.6.RELEASE</version> </dependency> <dependency> <groupId>quartz</groupId> <artifactId>quartz</artifactId> <version>1.5.2</version> </dependency> <dependency> <groupId>org.apache.ibatis</groupId> <artifactId>ibatis-sqlmap</artifactId> <version>2.3.4.726</version> </dependency> <!-- <dependency>--> <!-- <groupId>com.ibatis</groupId>--> <!-- <artifactId>ibatis2-sqlmap</artifactId>--> <!-- <version>2.1.7.597</version>--> <!-- </dependency>--> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency> <dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> <version>2.4</version> </dependency> <dependency> <groupId>commons-logging</groupId> <artifactId>commons-logging</artifactId> <version>1.2</version> </dependency> <dependency> <groupId>commons-lang</groupId> <artifactId>commons-lang</artifactId> <version>2.6</version> </dependency> <dependency> <groupId>commons-dbcp</groupId> <artifactId>commons-dbcp</artifactId> <version>1.4</version> </dependency> <dependency> <groupId>commons-pool</groupId> <artifactId>commons-pool</artifactId> <version>1.6</version> </dependency> <dependency> <groupId>commons-fileupload</groupId> <artifactId>commons-fileupload</artifactId> <version>1.3.1</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.35</version> </dependency> <dependency> <groupId>com.belerweb</groupId> <artifactId>pinyin4j</artifactId> <version>2.5.0</version> </dependency> <dependency> <groupId>jstl</groupId> <artifactId>jstl</artifactId> <version>1.2</version> </dependency> <dependency> <groupId>com.google.code.gson</groupId> <artifactId>gson</artifactId> <version>2.5</version> </dependency> <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> <version>4.4.1</version> </dependency> <dependency> <groupId>javax.mail</groupId> <artifactId>mail</artifactId> <version>1.5.0-b01</version> </dependency> <!-- 激光消息推送Starts --> <dependency> <groupId>cn.jpush.api</groupId> <artifactId>jpush-client</artifactId> <version>3.1.3</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.7.5</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>1.7.5</version> </dependency> <dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> <version>17.0</version> </dependency> <dependency> <groupId>com.squareup.okhttp</groupId> <artifactId>mockwebserver</artifactId> <version>1.5.4</version> <scope>test</scope> </dependency> <!-- 激光消息推送END --> <dependency> <groupId>org.apache.poi</groupId> <artifactId>poi</artifactId> <version>3.11</version> </dependency> <dependency> <groupId>net.sf.ehcache</groupId> <artifactId>ehcache</artifactId> <version>2.10.0</version> </dependency> <dependency> <groupId>javax.servlet.jsp</groupId> <artifactId>jsp-api</artifactId> <version>2.2</version> </dependency> <dependency> <groupId>com.lowagie</groupId> <artifactId>itext</artifactId> <version>2.1.7</version> </dependency> <!-- https://mvnrepository.com/artifact/commons-net/commons-net --> <dependency> <groupId>commons-net</groupId> <artifactId>commons-net</artifactId> <version>3.3</version> </dependency> <!-- https://mvnrepository.com/artifact/com.mchange/c3p0 --> <dependency> <groupId>com.mchange</groupId> <artifactId>c3p0</artifactId> <version>0.9.5.2</version> </dependency> <!-- https://mvnrepository.com/artifact/org.apache.ws.commons.axiom/axiom-api --> <dependency> <groupId>org.apache.ws.commons.axiom</groupId> <artifactId>axiom-api</artifactId> <version>1.2.13</version> </dependency> <!-- https://mvnrepository.com/artifact/dom4j/dom4j --> <dependency> <groupId>dom4j</groupId> <artifactId>dom4j</artifactId> <version>1.6.1</version> </dependency> <!-- https://mvnrepository.com/artifact/org.apache.axis/axis --> <dependency> <groupId>org.apache.axis</groupId> <artifactId>axis</artifactId> <version>1.4</version> </dependency> <!-- https://mvnrepository.com/artifact/javax.xml.rpc/javax.xml.rpc-api --> <dependency> <groupId>javax.xml.rpc</groupId> <artifactId>javax.xml.rpc-api</artifactId> <version>1.1.1</version> </dependency> <!-- https://mvnrepository.com/artifact/org.apache.axis2/axis2 --> <dependency> <groupId>org.apache.axis2</groupId> <artifactId>axis2</artifactId> <version>1.7.6</version> <type>pom</type> </dependency> <!-- https://mvnrepository.com/artifact/org.apache.axis2/axis2-adb --> <dependency> <groupId>org.apache.axis2</groupId> <artifactId>axis2-adb</artifactId> <version>1.7.6</version> </dependency> <!-- https://mvnrepository.com/artifact/soap/soap --> <dependency> <groupId>soap</groupId> <artifactId>soap</artifactId> <version>2.3</version> </dependency> <!-- https://mvnrepository.com/artifact/commons-httpclient/commons-httpclient --> <dependency> <groupId>commons-httpclient</groupId> <artifactId>commons-httpclient</artifactId> <version>3.1</version> </dependency> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.9.10.4</version> </dependency> <dependency> <groupId>org.eclipse.paho</groupId> <artifactId>org.eclipse.paho.client.mqttv3</artifactId> <version>1.2.0</version> </dependency> <dependency> <groupId>cn.hutool</groupId> <artifactId>hutool-all</artifactId> <version>5.7.2</version> </dependency> </dependencies> <build> <finalName>jdwlw</finalName> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.8</source> <target>1.8</target> <encoding>utf-8</encoding> <compilerArguments> <extdirs>${project.basedir}/src/main/webapp/WEB-INF/lib</extdirs> </compilerArguments> </configuration> </plugin> </plugins> <resources> <resource> <directory>src/main/resources</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>false</filtering> </resource> <resource> <directory>src/main/java</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>false</filtering> </resource> </resources> </build> </project> 依据上述代码解决报错:D:\biancheng\yf服务器代码\jdwlw>mvn clean package [INFO] Scanning for projects... [WARNING] [WARNING] Some problems were encountered while building the effective model for jdwlw:jdwlw:war:0.0.1-SNAPSHOT [WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 359, column 12 [WARNING] [WARNING] It is highly recommended to fix these problems because they threaten the stability of your build. [WARNING] [WARNING] For this reason, future Maven versions might no longer support building such malformed projects. [WARNING] [INFO] [INFO] ----------------------------< jdwlw:jdwlw >----------------------------- [INFO] Building maven Maven Webapp 0.0.1-SNAPSHOT [INFO] from pom.xml [INFO] --------------------------------[ war ]--------------------------------- Downloading from central: https://repo.maven.apache.org/maven2/com/google/code/ksoap2-android/ksoap2-android/3.6.4/ksoap2-android-3.6.4.pom [WARNING] The POM for com.google.code.ksoap2-android:ksoap2-android:jar:3.6.4 is missing, no dependency information available Downloading from central: https://repo.maven.apache.org/maven2/com/google/code/ksoap2-android/ksoap2-android/3.6.4/ksoap2-android-3.6.4.jar [INFO] ------------------------------------------------------------------------ [INFO] BUILD FAILURE [INFO] ------------------------------------------------------------------------ [INFO] Total time: 3.187 s [INFO] Finished at: 2025-06-30T19:08:28+08:00 [INFO] ------------------------------------------------------------------------ [ERROR] Failed to execute goal on project jdwlw: Could not resolve dependencies for project jdwlw:jdwlw:war:0.0.1-SNAPSHOT: Could not find artifact com.google.code.ksoap2-android:ksoap2-android:jar:3.6.4 in central (https://repo.maven.apache.org/maven2) -> [Help 1] [ERROR] [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch. [ERROR] Re-run Maven using the -X switch to enable full debug logging. [ERROR] [ERROR] For more information about the errors and possible solutions, please read the following articles: [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/DependencyResolutionException
最新发布
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