Service插件化解决方案

--摘自《android插件化开发指南》

1.ActivityThread最终是通过Instrumentation启动一个Activity的。而ActivityThread启动Service并不借助于Instrumentation，而是直接把Service反射出来就启动了。Instrumentation只给Activity提供服务

2.一般预先在宿主app中创建10个StubService占位就够了

***startService的解决方案***

首先把插件和宿主的dex合并

/**
 * 由于应用程序使用的ClassLoader为PathClassLoader
 * 最终继承自 BaseDexClassLoader
 * 查看源码得知,这个BaseDexClassLoader加载代码根据一个叫做
 * dexElements的数组进行, 因此我们把包含代码的dex文件插入这个数组
 * 系统的classLoader就能帮助我们找到这个类
 *
 * 这个类用来进行对于BaseDexClassLoader的Hook
 * 类名太长, 不要吐槽.
 * @author weishu
 * @date 16/3/28
 */
public final class BaseDexClassLoaderHookHelper {

    public static void patchClassLoader(ClassLoader cl, File apkFile, File optDexFile)
            throws IllegalAccessException, NoSuchMethodException, IOException, InvocationTargetException, InstantiationException, NoSuchFieldException {
        // 获取 BaseDexClassLoader : pathList
        Object pathListObj = RefInvoke.getFieldObject(DexClassLoader.class.getSuperclass(), cl, "pathList");

        // 获取 PathList: Element[] dexElements
        Object[] dexElements = (Object[]) RefInvoke.getFieldObject(pathListObj, "dexElements");

        // Element 类型
        Class<?> elementClass = dexElements.getClass().getComponentType();

        // 创建一个数组, 用来替换原始的数组
        Object[] newElements = (Object[]) Array.newInstance(elementClass, dexElements.length + 1);

        // 构造插件Element(File file, boolean isDirectory, File zip, DexFile dexFile) 这个构造函数
        Class[] p1 = {File.class, boolean.class, File.class, DexFile.class};
        Object[] v1 = {apkFile, false, apkFile, DexFile.loadDex(apkFile.getCanonicalPath(), optDexFile.getAbsolutePath(), 0)};
        Object o = RefInvoke.createObject(elementClass, p1, v1);

        Object[] toAddElementArray = new Object[] { o };
        // 把原始的elements复制进去
        System.arraycopy(dexElements, 0, newElements, 0, dexElements.length);
        // 插件的那个element复制进去
        System.arraycopy(toAddElementArray, 0, newElements, dexElements.length, toAddElementArray.length);

        // 替换
        RefInvoke.setFieldObject(pathListObj, "dexElements", newElements);
    }
}

其次采用“欺上瞒下”的方法

public class AMSHookHelper {

    public static final String EXTRA_TARGET_INTENT = "extra_target_intent";

    public static void hookAMN() throws ClassNotFoundException,
            NoSuchMethodException, InvocationTargetException,
            IllegalAccessException, NoSuchFieldException {

        //获取AMN的gDefault单例gDefault，gDefault是final静态的
        Object gDefault = RefInvoke.getStaticFieldObject("android.app.ActivityManagerNative", "gDefault");

        // gDefault是一个 android.util.Singleton<T>对象; 我们取出这个单例里面的mInstance字段
        Object mInstance = RefInvoke.getFieldObject("android.util.Singleton", gDefault, "mInstance");

        // 创建一个这个对象的代理对象MockClass1, 然后替换这个字段, 让我们的代理对象帮忙干活
        Class<?> classB2Interface = Class.forName("android.app.IActivityManager");
        Object proxy = Proxy.newProxyInstance(
                Thread.currentThread().getContextClassLoader(),
                new Class<?>[] { classB2Interface },
                new MockClass1(mInstance));

        //把gDefault的mInstance字段，修改为proxy
        Class class1 = gDefault.getClass();
        RefInvoke.setFieldObject("android.util.Singleton", gDefault, "mInstance", proxy);
    }

    public static void hookActivityThread() throws Exception {

        // 先获取到当前的ActivityThread对象
        Object currentActivityThread = RefInvoke.getStaticFieldObject("android.app.ActivityThread", "sCurrentActivityThread");

        // 由于ActivityThread一个进程只有一个,我们获取这个对象的mH
        Handler mH = (Handler) RefInvoke.getFieldObject(currentActivityThread, "mH");

        //把Handler的mCallback字段，替换为new MockClass2(mH)
        RefInvoke.setFieldObject(Handler.class, mH, "mCallback", new MockClass2(mH));
    }
}

其中，HookService，让AMS启动StubService的实现在类MockClass1上

class MockClass1 implements InvocationHandler {

    private static final String TAG = "MockClass1";

    // 替身StubService的包名
    private static final String stubPackage = "jianqiang.com.activityhook1";

    Object mBase;

    public MockClass1(Object base) {
        mBase = base;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        Log.e("bao", method.getName());

        if ("startService".equals(method.getName())) {
            // 只拦截这个方法
            // 替换参数, 任你所为;甚至替换原始StubService启动别的Service偷梁换柱

            // 找到参数里面的第一个Intent 对象
            int index = 0;
            for (int i = 0; i < args.length; i++) {
                if (args[i] instanceof Intent) {
                    index = i;
                    break;
                }
            }

            //get StubService form UPFApplication.pluginServices
            Intent rawIntent = (Intent) args[index];
            String rawServiceName = rawIntent.getComponent().getClassName();

            String stubServiceName = UPFApplication.pluginServices.get(rawServiceName);

            // replace Plugin Service of StubService
            ComponentName componentName = new ComponentName(stubPackage, stubServiceName);
            Intent newIntent = new Intent();
            newIntent.setComponent(componentName);

            // Replace Intent, cheat AMS
            args[index] = newIntent;

            Log.d(TAG, "hook success");
            return method.invoke(mBase, args);
        } else if ("stopService".equals(method.getName())) {
            // 只拦截这个方法
            // 替换参数, 任你所为;甚至替换原始StubService启动别的Service偷梁换柱

            // 找到参数里面的第一个Intent 对象
            int index = 0;
            for (int i = 0; i < args.length; i++) {
                if (args[i] instanceof Intent) {
                    index = i;
                    break;
                }
            }

            //get StubService form UPFApplication.pluginServices
            Intent rawIntent = (Intent) args[index];
            String rawServiceName = rawIntent.getComponent().getClassName();
            String stubServiceName = UPFApplication.pluginServices.get(rawServiceName);

            // replace Plugin Service of StubService
            ComponentName componentName = new ComponentName(stubPackage, stubServiceName);
            Intent newIntent = new Intent();
            newIntent.setComponent(componentName);

            // Replace Intent, cheat AMS
            args[index] = newIntent;

            Log.d(TAG, "hook success");
            return method.invoke(mBase, args);
        }

        return method.invoke(mBase, args);
    }
}

第2，AMS被欺骗后，它原本会通知APP启动StubService，而我们要Hook掉ActivityThread的mH对象的mCallback对象，仍然截获它的handleMessage方法（handleCreateService方法），具体实现在MockClass2中

class MockClass2 implements Handler.Callback {

    Handler mBase;

    public MockClass2(Handler base) {
        mBase = base;
    }

    @Override
    public boolean handleMessage(Message msg) {

        Log.d("baobao4321", String.valueOf(msg.what));
        switch (msg.what) {

            // ActivityThread里面 "CREATE_SERVICE" 这个字段的值是114
            // 本来使用反射的方式获取最好, 这里为了简便直接使用硬编码
            case 114:
                handleCreateService(msg);
                break;
        }

        mBase.handleMessage(msg);
        return true;
    }

    private void handleCreateService(Message msg) {
        // 这里简单起见,直接取出插件Servie

        Object obj = msg.obj;
        ServiceInfo serviceInfo = (ServiceInfo) RefInvoke.getFieldObject(obj, "info");

        String realServiceName = null;

        for (String key : UPFApplication.pluginServices.keySet()) {
            String value = UPFApplication.pluginServices.get(key);
            if(value.equals(serviceInfo.name)) {
                realServiceName = key;
                break;
            }
        }

        serviceInfo.name = realServiceName;
    }
}

在宿主中调用

Intent intent = new Intent();
intent.setComponent(
        new ComponentName("jianqiang.com.testservice1",
                "jianqiang.com.testservice1.MyService1"));
startService(intent);

Intent intent = new Intent();
intent.setComponent(
        new ComponentName("jianqiang.com.testservice1",
                "jianqiang.com.testservice1.MyService1"));
stopService(intent);

***bindService的解决方案***

只要在实现类MockClass1中增加

else if ("bindService".equals(method.getName())) {

    // 找到参数里面的第一个Intent 对象
    int index = 0;
    for (int i = 0; i < args.length; i++) {
        if (args[i] instanceof Intent) {
            index = i;
            break;
        }
    }

    Intent rawIntent = (Intent) args[index];
    String rawServiceName = rawIntent.getComponent().getClassName();
    String stubServiceName = UPFApplication.pluginServices.get(rawServiceName);

    // replace Plugin Service of StubService
    ComponentName componentName = new ComponentName(stubPackage, stubServiceName);
    Intent newIntent = new Intent();
    newIntent.setComponent(componentName);

    // Replace Intent, cheat AMS
    args[index] = newIntent;

    Log.d(TAG, "hook success");
    return method.invoke(mBase, args);
}

宿主中调用

Intent intent = new Intent();
intent.setComponent(
        new ComponentName("jianqiang.com.testservice1",
                "jianqiang.com.testservice1.MyService2"));
bindService(intent, conn, Service.BIND_AUTO_CREATE);

unbindService(conn);

问1：为什么不在unbind的时候欺骗AMS？

因为unbind语法是unbindService(conn)，AMS会根据conn来找到对应的Service，所以我们不需要把MyService2替换为StubService2

问2：为什么在MockClass2中不需要吧StubService2切换回MyService2？

因为bindService是先走handleCreateService再走handleBindService方法。在handleCreateService方法中已经将StubService2切换回MyService2了，所以后面不需要切换了。

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