插件化DroidPlugin-Provider

主要思想

host预先申请若干stubProvider
hook ams，插件查询provider时，返回stubProVider
在 stubProvider 中操控插件的providr对象

Provider 查询

源码关键路径分析

getContext().getContentResolver().XXX最终会调用到ActivityThread的acquireProvider方法

public final IContentProvider acquireProvider( Context c, String auth ...）{
    final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);
    if (provider != null) {
        return provider;
    }
    //查询AMS
    holder = ActivityManagerNative.getDefault().getContentProvider(
                getApplicationThread(), auth, userId, stable);
    return holder.provider;
}

系统先到调用acquireExistingProvider方法查询，如果有返回。没有，查询AMS。很明显，acquireExistingProvider方法应该是查了缓存

public final IContentProvider acquireExistingProvider(）{
    //果然只查了个缓存。
    final ProviderClientRecord pr = mProviderMap.get(key);
    if (pr == null) return null;
    IContentProvider provider = pr.mProvider;
    return provider;
}

这里有两种hook方案，一种是DroidPlugin的方法，hook掉AMS的getContentProvider方法，另外是把插件的provider信息直接放到缓存mProviderMap中。
以hook掉AMS的getContentProvider方法为准

hook AMS getContentProvider

在IActivityManagerHookHandle类中登记hook方法:

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protected void init() {
    sHookedMethodHandlers.put("getContentProvider", new getContentProvider(mHostContext));
}

看hook方案的实现

protected boolean beforeInvoke(Object receiver, Method method, Object[] args){
    String authority=(String) args[1];
    //找到插件的provider记录
    mTargetProvider = PluginManager.getInstance().resolveContentProvider(PluginProcessManager.getCurrentVUid(), name, 0);
    //分配一个provider坑
    mStubProvider = PluginManager.getInstance().selectStubProviderInfo(mTargetProvider, name);
    //替换参数中的，让系统启动 stubProvider
    args[index] = mStubProvider.authority;
}

stubProvider 实现

onCreate

先看增删改查的出处理
/** AbstractContentProviderStub **/
public Cursor query(Uri uri, String[] projection,
                    String selection, String[] selectionArgs, String sortOrder) {
    String targetAuthority = uri.getQueryParameter(Env.EXTRA_TARGET_AUTHORITY);
    //拿到插件provider的对象
    ContentProviderClient client = getContentProviderClient(targetAuthority);
    //返回插件provider的执行结果
    return client.query(buildNewUri(uri, targetAuthority), projection, selection, selectionArgs, sortOrder);
}

继续看getContentProviderClient函数

private synchronized ContentProviderClient getContentProviderClient(final String     targetAuthority) {
    ContentProviderClient client = sClients.get(targetAuthority);
    if (client != null) {
        return client;
    }
    //..
}

sClient是一个map,很明显，这又是一个cache。cache中存储了插件provider的信息。继续看存储信息的时机。

加载provider信息
在PluginProcessManager类中，有个preLoadApk方法

private static void preLoadApk(Context hostContext, String packageName) {
    Application application = applicationMap.get(packageName);
    installContentProviders(hostContext, application, packageName);
}

根据插件的packageName拿到插件的Application，继续看installContentProviders方法

private static void installContentProviders(Context hostContext, Application app, String packageName) {
    //获得stubProvider引用
    AbstractContentProviderStub proxy = AbstractContentProviderStub.getProxyInstance();
    //插件pkgInfo
    PackageInfo pkgInfo = PluginManager.getInstance().getPackageInfo(packageName, PackageManager.GET_PROVIDERS);
    for (ProviderInfo providerInfo : pkgInfo.providers) {
        //获取满足条件的插件的providr
        ContentProviderClient localProvider = app.getContentResolver().acquireContentProviderClient(providerInfo.authority);
        //绑定stubProvider
        proxy.installClient(providerInfo, localProvider);
    }
}

AbstractContentProviderStub.getProxyInstance()返回的是stubProvider的引用

/** AbstractContentProviderStub **/
public boolean onCreate() {
    sProxy = this;
}

public static AbstractContentProviderStub getProxyInstance() {
    return sProxy;
}

最后，看proxy.installClient方法，方法只将插件的provider放到缓存中

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public void installClient(ProviderInfo info, ContentProviderClient provider) {
    sClients.put(info.authority, provider);
}

至此，provider插件化分析完毕

小结

在插件加载时，程序缓存了插件pkg信息
插件查询provider时，返回一个预先申请好的stubProvider
将stubProvider与插件的provider绑定在一起，由stubProvider操控插件的provider

参考：