Android动态部署五：怎样从插件apk中启动Service

转载请注明出处：http://blog.csdn.net/ximsfei/article/details/51072332

github地址：https://github.com/ximsfei/DynamicDeploymentApk

Android动态部署一：Google原生Split APK浅析
Android动态部署二：APK安装及AndroidManifest.xml解析流程分析
Android动态部署三：怎样从插件apk中启动Activity（一）
Android动态部署四：怎样从插件apk中启动Activity（二）

经过前面几篇文章的分析，我们了解到了Google原生是怎样拆分apk的。而且我们自己能够通过解析manifest文件。通过创建插件ClassLoader，Resources对象来启动插件APK中的Activity，上一篇文章关于资源的问题，有一点遗漏，在插件中开发人员有可能通过例如以下代码获取资源Id
getIdentifier("xxx", "layout", getPackageName());
此时调用getPackageName()方法返回的是宿主apk的包名，所以我们须要在DynamicContextImpl类中重写getPackageName()方法，返回从插件apk的manifest中解析出来的的包名。接下来我们通过分析Service启动流程来看看宿主apk怎样启动Android四大组件之Service。

Service启动流程

startService(new Intent(this, TargetService.class));

在Activity中，非常easy的一行代码，就能够启动TargetService了，下图就是调用这行代码后的时序图：

带着成功启动插件Activity的经验，我们继续通过分析Service启动流程。试图从中找到hook点从而将我们对插件Service的扩展操作，通过相似的重写DynamicInstrumentation类。替换进ActivityThread中。
在时序图中我们发如今调用startService方法后，终于都会调到ContextImpl中的startService。

@Override
public ComponentName startService(Intent service) {
    warnIfCallingFromSystemProcess();
    return startServiceCommon(service, mUser);
}

private ComponentName startServiceCommon(Intent service, UserHandle user) {
    try {
        validateServiceIntent(service);
        service.prepareToLeaveProcess();
        ComponentName cn = ActivityManagerNative.getDefault().startService(
            mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
                        getContentResolver()), getOpPackageName(), user.getIdentifier());
        if (cn != null) {
            if (cn.getPackageName().equals("!")) {
                throw new SecurityException(
                        "Not allowed to start service " + service
                        + " without permission " + cn.getClassName());
            } else if (cn.getPackageName().equals("!!")) {
                throw new SecurityException(
                        "Unable to start service " + service
                        + ": " + cn.getClassName());
            }
        }
        return cn;
    } catch (RemoteException e) {
        throw new RuntimeException("Failure from system", e);
    }
}

在看了源代码之后我们发现，这种方法的功能，事实上跟Activity启动流程中Instrumentation类中的execStartActivity方法相似，看到这就感觉启动插件Service已经十拿九稳了，我们已经跨出了非常大的一步。我们继续来深入研究Service的启动流程的源代码：
ActiveServices.java

private final String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean execInFg,
        boolean whileRestarting) throws TransactionTooLargeException {
    if (r.app != null && r.app.thread != null) {
        sendServiceArgsLocked(r, execInFg, false);//假设Service已启动，在这里会直接调用Service的onStartCommand方法
        return null;
    }

    if (!whileRestarting && r.restartDelay > 0) {
        // If waiting for a restart, then do nothing.
        return null;
    }

    if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Bringing up " + r + " " + r.intent);

    // We are now bringing the service up, so no longer in the
    // restarting state.
    if (mRestartingServices.remove(r)) {
        r.resetRestartCounter();
        clearRestartingIfNeededLocked(r);
    }

    // Make sure this service is no longer considered delayed, we are starting it now.
    if (r.delayed) {
        if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE, "REM FR DELAY LIST (bring up): " + r);
        getServiceMap(r.userId).mDelayedStartList.remove(r);
        r.delayed = false;
    }

    // Make sure that the user who owns this service is started.  If not,
    // we don‘t want to allow it to run.
    if (mAm.mStartedUsers.get(r.userId) == null) {
        String msg = "Unable to launch app "
                + r.appInfo.packageName + "/"
                + r.appInfo.uid + " for service "
                + r.intent.getIntent() + ": user " + r.userId + " is stopped";
        Slog.w(TAG, msg);
        bringDownServiceLocked(r);
        return msg;
    }

    // Service is now being launched, its package can‘t be stopped.
    try {
        AppGlobals.getPackageManager().setPackageStoppedState(
                r.packageName, false, r.userId);
    } catch (RemoteException e) {
    } catch (IllegalArgumentException e) {
        Slog.w(TAG, "Failed trying to unstop package "
                + r.packageName + ": " + e);
    }

    final boolean isolated = (r.serviceInfo.flags&ServiceInfo.FLAG_ISOLATED_PROCESS) != 0;
    final String procName = r.processName;
    ProcessRecord app;

    if (!isolated) {
        app = mAm.getProcessRecordLocked(procName, r.appInfo.uid, false);
        if (DEBUG_MU) Slog.v(TAG_MU, "bringUpServiceLocked: appInfo.uid=" + r.appInfo.uid
                    + " app=" + app);
        if (app != null && app.thread != null) {
            try {
                app.addPackage(r.appInfo.packageName, r.appInfo.versionCode, mAm.mProcessStats);
                realStartServiceLocked(r, app, execInFg); //这里会真正启动Service
                return null;
            } catch (TransactionTooLargeException e) {
                throw e;
            } catch (RemoteException e) {
                Slog.w(TAG, "Exception when starting service " + r.shortName, e);
            }

            // If a dead object exception was thrown -- fall through to
            // restart the application.
        }
    } else {
        // If this service runs in an isolated process, then each time
        // we call startProcessLocked() we will get a new isolated
        // process, starting another process if we are currently waiting
        // for a previous process to come up.  To deal with this, we store
        // in the service any current isolated process it is running in or
        // waiting to have come up.
        app = r.isolatedProc;
    }

    // Not running -- get it started, and enqueue this service record
    // to be executed when the app comes up.
    if (app == null) {
        if ((app=mAm.startProcessLocked(procName, r.appInfo, true, intentFlags,
                "service", r.name, false, isolated, false)) == null) {
            String msg = "Unable to launch app "
                    + r.appInfo.packageName + "/"
                    + r.appInfo.uid + " for service "
                    + r.intent.getIntent() + ": process is bad";
            Slog.w(TAG, msg);
            bringDownServiceLocked(r);
            return msg;
        }
        if (isolated) {
            r.isolatedProc = app;
        }
    }

    if (!mPendingServices.contains(r)) {
        mPendingServices.add(r);
    }

    if (r.delayedStop) {
        // Oh and hey we‘ve already been asked to stop!
        r.delayedStop = false;
        if (r.startRequested) {
            if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE,
                    "Applying delayed stop (in bring up): " + r);
            stopServiceLocked(r);
        }
    }

    return null;
}

private final void sendServiceArgsLocked(ServiceRecord r, boolean execInFg,
        boolean oomAdjusted) throws TransactionTooLargeException {
    ...

    while (r.pendingStarts.size() > 0) {
        ...
        try {
            ...
            r.app.thread.scheduleServiceArgs(r, si.taskRemoved, si.id, flags, si.intent);
        } catch (Exception e) {
        }
        ...
    }
    ...
}

private final void realStartServiceLocked(ServiceRecord r,
        ProcessRecord app, boolean execInFg) throws RemoteException {
    if (app.thread == null) {
        throw new RemoteException();
    }
    ...
    r.app = app;
    r.restartTime = r.lastActivity = SystemClock.uptimeMillis();

    final boolean newService = app.services.add(r);
    bumpServiceExecutingLocked(r, execInFg, "create");
    mAm.updateLruProcessLocked(app, false, null);
    mAm.updateOomAdjLocked();

    boolean created = false;
    try {
        if (LOG_SERVICE_START_STOP) {
            String nameTerm;
            int lastPeriod = r.shortName.lastIndexOf(‘.‘);
            nameTerm = lastPeriod >= 0 ? r.shortName.substring(lastPeriod) : r.shortName;
            EventLogTags.writeAmCreateService(
                    r.userId, System.identityHashCode(r), nameTerm, r.app.uid, r.app.pid);
        }
        synchronized (r.stats.getBatteryStats()) {
            r.stats.startLaunchedLocked();
        }
        mAm.ensurePackageDexOpt(r.serviceInfo.packageName);
        app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
        app.thread.scheduleCreateService(r, r.serviceInfo,
                mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
                app.repProcState);// 相似Activity启动流程中的app.thread.scheduleLaunchActivity方法。在这里会new一个Service。而且调用attach以及onCreate方法
        r.postNotification();
        created = true;
    } catch (DeadObjectException e) {
        Slog.w(TAG, "Application dead when creating service " + r);
        mAm.appDiedLocked(app);
        throw e;
    } finally {
        if (!created) {
            // Keep the executeNesting count accurate.
            final boolean inDestroying = mDestroyingServices.contains(r);
            serviceDoneExecutingLocked(r, inDestroying, inDestroying);

            // Cleanup.
            if (newService) {
                app.services.remove(r);
                r.app = null;
            }

            // Retry.
            if (!inDestroying) {
                scheduleServiceRestartLocked(r, false);
            }
        }
    }

    requestServiceBindingsLocked(r, execInFg);

    updateServiceClientActivitiesLocked(app, null, true);

    // If the service is in the started state, and there are no
    // pending arguments, then fake up one so its onStartCommand() will
    // be called.
    if (r.startRequested && r.callStart && r.pendingStarts.size() == 0) {
        r.pendingStarts.add(new ServiceRecord.StartItem(r, false, r.makeNextStartId(),
                null, null));
    }

    sendServiceArgsLocked(r, execInFg, true);//第一次启动的Service，会在这里调用onStartCommand方法

    if (r.delayed) {
        if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE, "REM FR DELAY LIST (new proc): " + r);
        getServiceMap(r.userId).mDelayedStartList.remove(r);
        r.delayed = false;
    }

    if (r.delayedStop) {
        // Oh and hey we‘ve already been asked to stop!
        r.delayedStop = false;
        if (r.startRequested) {
            if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE,
                    "Applying delayed stop (from start): " + r);
            stopServiceLocked(r);
        }
    }
}

ActivityThread.java

//ActivityThread$ApplicationThread
public final void scheduleServiceArgs(IBinder token, boolean taskRemoved, int startId,
    int flags ,Intent args) {
    ...
    sendMessage(H.SERVICE_ARGS, s);
}

public final void scheduleCreateService(IBinder token,
        ServiceInfo info, CompatibilityInfo compatInfo, int processState) {
    ...
    sendMessage(H.CREATE_SERVICE, s);
}

//ActivityThread$H
public void handleMessage(Message msg) {
    switch (msg.what) {
        case CREATE_SERVICE: {
            handleCreateService((CreateServiceData)msg.obj);
        } break;
        case SERVICE_ARGS: {
            handleServiceArgs((ServiceArgsData)msg.obj);
        } break;
    }
}

//ActivityThread
private void handleCreateService(CreateServiceData data) {
    ...

    LoadedApk packageInfo = getPackageInfoNoCheck(
            data.info.applicationInfo, data.compatInfo);
    Service service = null;
    try {
        java.lang.ClassLoader cl = packageInfo.getClassLoader();
        service = (Service) cl.loadClass(data.info.name).newInstance();//这里和Activity的启动流程有些许区别
    } catch (Exception e) {
        if (!mInstrumentation.onException(service, e)) {
            throw new RuntimeException(
                "Unable to instantiate service " + data.info.name
                + ": " + e.toString(), e);
        }
    }

    try {
        if (localLOGV) Slog.v(TAG, "Creating service " + data.info.name);

        ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
        context.setOuterContext(service);

        Application app = packageInfo.makeApplication(false, mInstrumentation);
        service.attach(context, this, data.info.name, data.token, app,
                ActivityManagerNative.getDefault());
        service.onCreate();//这里直接调用了onCreate，而没有相似的先调用callActivityOnCreate方法
        mServices.put(data.token, service);
        try {
            ActivityManagerNative.getDefault().serviceDoneExecuting(
                    data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
        } catch (RemoteException e) {
            // nothing to do.
        }
    } catch (Exception e) {
        if (!mInstrumentation.onException(service, e)) {
            throw new RuntimeException(
                "Unable to create service " + data.info.name
                + ": " + e.toString(), e);
        }
    }
}

private void handleServiceArgs(ServiceArgsData data) {
    Service s = mServices.get(data.token);
    if (s != null) {
        try {
            if (data.args != null) {
                data.args.setExtrasClassLoader(s.getClassLoader());
                data.args.prepareToEnterProcess();
            }
            int res;
            if (!data.taskRemoved) {
                res = s.onStartCommand(data.args, data.flags, data.startId);
            } else {
                s.onTaskRemoved(data.args);
                res = Service.START_TASK_REMOVED_COMPLETE;
            }

            QueuedWork.waitToFinish();

            try {
                ActivityManagerNative.getDefault().serviceDoneExecuting(
                        data.token, SERVICE_DONE_EXECUTING_START, data.startId, res);
            } catch (RemoteException e) {
                // nothing to do.
            }
            ensureJitEnabled();
        } catch (Exception e) {
            if (!mInstrumentation.onException(s, e)) {
                throw new RuntimeException(
                        "Unable to start service " + s
                        + " with " + data.args + ": " + e.toString(), e);
            }
        }
    }
}

看到这里。原生Service也启动起来了，我们发现Service的启动流程和Activity的相似。但又不全然一样，正是由于这些许区别。让我们的开发工作陷入了困境，遇到了以下这些“坑”：
1. Service不像Activity的标准模式，能够一直实例化，当某个Service启动后，从上面的代码能够看到，再次调用startService方法。源代码中并不会去又一次创建Service。调用onCreate，而是直接调用onStartCommand方法，所以我们不能通过StubService的方式来启动插件Service。
2. Service的handleCreateService方法不像在Activity启动流程中的performLaunchActivity方法中获取类名后，通过Instrumentation类的newActivity方法实例化，通过callActivityOnCreate方法间接调用Activity的onCreate，这样我们有机会通过重写DynamicInstrumentation类来扩展插件功能。而Service却直接在ActivityThread类中实例化。而且在attach方法结束后直接调用onCreate方法。

private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    ...
    Activity a = performLaunchActivity(r, customIntent);
    ...
}

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    ActivityInfo aInfo = r.activityInfo;
    if (r.packageInfo == null) {
        r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
                Context.CONTEXT_INCLUDE_CODE);
    }
    ...
    Activity activity = null;
    try {
        java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
        activity = mInstrumentation.newActivity(
                cl, component.getClassName(), r.intent);
        ...
    } catch (Exception e) {
        ...
    }

    try {
        ...
        if (activity != null) {
            ...
            activity.attach(appContext, this, getInstrumentation(), r.token,
                    r.ident, app, r.intent, r.activityInfo, title, r.parent,
                    r.embeddedID, r.lastNonConfigurationInstances, config,
                    r.referrer, r.voiceInteractor);
            ...
            if (r.isPersistable()) {
                mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
            } else {
                mInstrumentation.callActivityOnCreate(activity, r.state);
            }
            ...
        }
    } catch (Exception e) {
        ...
    }
    return activity;
}

上面那两个坑，恰恰是我们在实现从插件apk中启动Activity时所关注的点。似乎这些点在这里一个都用不上，前面跨出的一大步，感觉也是被打了回去，在接下来的几天里。我重复阅读源代码，发现了当中的一个关键点。插件中的Service是使用插件的ClassLoader通过类名来载入的。那我们能够在ClassLoader上做一些“手脚”。

private void handleCreateService(CreateServiceData data) {
    ...
    LoadedApk packageInfo = getPackageInfoNoCheck(
            data.info.applicationInfo, data.compatInfo);
    Service service = null;
    try {
        java.lang.ClassLoader cl = packageInfo.getClassLoader();
        service = (Service) cl.loadClass(data.info.name).newInstance();
    } catch (Exception e) {
        ...
    }
    ...
}

public final LoadedApk getPackageInfoNoCheck(ApplicationInfo ai,
        CompatibilityInfo compatInfo) {
    return getPackageInfo(ai, compatInfo, null, false, true, false);
}

private LoadedApk getPackageInfo(ApplicationInfo aInfo, CompatibilityInfo compatInfo,
        ClassLoader baseLoader, boolean securityViolation, boolean includeCode,
        boolean registerPackage) {
    ...
    synchronized (mResourcesManager) {
        WeakReference<LoadedApk> ref;
        if (differentUser) {
            // Caching not supported across users
            ref = null;
        } else if (includeCode) {
            ref = mPackages.get(aInfo.packageName);//宿主apk的LoadApk保存在mPackages中
        } else {
            ref = mResourcePackages.get(aInfo.packageName);
        }

        LoadedApk packageInfo = ref != null ? ref.get() : null;
        if (packageInfo == null || (packageInfo.mResources != null
                && !packageInfo.mResources.getAssets().isUpToDate())) {
            if (localLOGV) Slog.v(TAG, (includeCode ?
 "Loading code package "
                    : "Loading resource-only package ") + aInfo.packageName
                    + " (in " + (mBoundApplication != null
                            ?
 mBoundApplication.processName : null)
                    + ")");
            packageInfo =
                new LoadedApk(this, aInfo, compatInfo, baseLoader,
                        securityViolation, includeCode &&
                        (aInfo.flags&ApplicationInfo.FLAG_HAS_CODE) != 0, registerPackage);

            if (mSystemThread && "android".equals(aInfo.packageName)) {
                packageInfo.installSystemApplicationInfo(aInfo,
                        getSystemContext().mPackageInfo.getClassLoader());
            }

            if (differentUser) {
                // Caching not supported across users
            } else if (includeCode) {
                mPackages.put(aInfo.packageName,
                        new WeakReference<LoadedApk>(packageInfo));
            } else {
                mResourcePackages.put(aInfo.packageName,
                        new WeakReference<LoadedApk>(packageInfo));
            }
        }
        return packageInfo;
    }
}

看到这个点之后，感觉像是抓住一个救命稻草那样兴奋，我们能够在每次安装一个插件apk的同一时候将插件apk的ClassLoader安装到mPackages.get(“host package name”)中。这样就能够不做其它的改动。依据插件apk中的Service类名就能够载入TargetService了，同一时候细心的读者也会发现，事实上Activity，BroadcastReceiver，ContentProvider也是通过这种方式载入的。真是一劳永逸呢。

DynamicClassLoaderWrapper.java

package com.ximsfei.dynamic.app;

import java.util.ArrayList;

/**
 * Created by pengfenx on 3/15/2016.
 */
public class DynamicClassLoaderWrapper extends ClassLoader {
    private final ClassLoader mBase;
    private final ArrayList<ClassLoader> mDynamicLoaders = new ArrayList<>();

    protected DynamicClassLoaderWrapper(ClassLoader base) {
        super();
        mBase = base;
    }

    public void addClassLoader(ClassLoader cl) {
        if (!mDynamicLoaders.contains(cl)) {
            mDynamicLoaders.add(cl);
        }
    }

    @Override
    protected Class<?> findClass(String className) throws ClassNotFoundException {
        try {
            return mBase.loadClass(className);
        } catch (ClassNotFoundException e) {
        }

        int N = mDynamicLoaders.size();
        for (int i=0; i<N; i++) {
            try {
                return mDynamicLoaders.get(i).loadClass(className);
            } catch (ClassNotFoundException e) {
            }//这里用try catch来推断该插件中是否存在TargetService不是非常好
        }
        throw new ClassNotFoundException(className);
    }

}

安装ClassLoader:

public synchronized void installClassLoader(ClassLoader classLoader) {
    Object loadedApk = ((WeakReference) getPackages().get(getHostPackageName())).get();
    try {
        ClassLoader cl = Reflect.create(loadedApk.getClass())
                .setMethod("getClassLoader").invoke(loadedApk);
        if (!(cl instanceof DynamicClassLoaderWrapper)) {
            DynamicClassLoaderWrapper dclw = new DynamicClassLoaderWrapper(cl);
            dclw.addClassLoader(classLoader);
            Reflect.create(loadedApk.getClass()).setField("mClassLoader")
                    .set(loadedApk, dclw);
        } else {
            ((DynamicClassLoaderWrapper) cl).addClassLoader(classLoader);
        }
    } catch (Exception e) {
    }
}

private synchronized Map getPackages() {
    if (mPackages == null) {
        try {
            mPackages = mActivityThreadReflect.setField("mPackages").get(currentActivityThread());
        } catch (Exception e) {
        }
    }
    return mPackages;
}

stopService, bindService, unbindService的流程与startService流程相似，而且不须要做过多的改动，在这里就不再分析了，有兴趣的读者能够自己去看一下源代码，分析一下。

遗留问题

第一个坑中，Service仅仅能启动一次，所以我们不能通过伪装成StubService的方式。来“骗过”AndroidManifest的检測，我也没有想到更好的方法来实现，临时仅仅能将要使用的Service类名注冊到宿主apk的AndroidManifest中来实现，假设读者有什么好的方法，能够分享出来一起学习一下。