Android开发— 热修复Tinker源码的简单介绍

0.  前言

热修复这项技术，基本上已经成为Android项目比较重要的模块了。主要因为项目在上线之后，都难免会有各种问题，而依靠发版去修复问题，成本太高了。

现在热修复的技术基本上有阿里的AndFix、QZone的方案、美团提出的思想方案以及腾讯的Tinker等。

其中AndFix可能接入是最简单的一个（和Tinker命令行接入方式差不多），不过AndFix兼容性有一定的问题，QZone方案对性能会有一定的影响，且在Art模式下出现内存错乱的问题，美团提出的思想方案主要是基于Instant Run的原理，目前尚未开源，兼容性较好。

这么看来，如果选择开源方案，Tinker目前是最佳的选择，下面来看看Tinker的大致的原理分析。

1. 原理概述

Tinker将old.apk和new.apk做了diff，拿到patch.dex后将其与本机中apk的classes.dex做了合并，生成新的classes.dex，运行时通过反射将合并后的dex文件放置在加载的dexElements数组的前面。

运行时替代的原理，其实和Qzone的方案差不多，都是去反射修改dexElements。两者的差异是：Qzone是直接将patch.dex插到数组的前面；而Tinker是合并后的全量dex插在数组的前面。因为Qzone方案中提到的CLASS_ISPREVERIFIED的解决方案存在问题。

Android的ClassLoader体系中加载类一般使用的是PathClassLoader和DexClassLoader，大家只需要明白，Android使用PathClassLoader作为其类加载器，DexClassLoader可以从.jar和.apk类型的文件内部加载classes.dex文件就好了。对于加载类，无非是给个classname，然后去findClass，PathClassLoader和DexClassLoader都继承自BaseDexClassLoader。在BaseDexClassLoader中有如下源码：

#BaseDexClassLoader
@Override
protected Class<?> findClass(String name) throws ClassNotFoundException {
    Class clazz = pathList.findClass(name);

    if (clazz == null) {
        throw new ClassNotFoundException(name);
    }

    return clazz;
}

#DexPathList
public Class findClass(String name) {
    for (Element element : dexElements) {
        DexFile dex = element.dexFile;

        if (dex != null) {
            Class clazz = dex.loadClassBinaryName(name, definingContext);
            if (clazz != null) {
                return clazz;
            }
        }
    }

    return null;
}

#DexFile
public Class loadClassBinaryName(String name, ClassLoader loader) {
    return defineClass(name, loader, mCookie);
}
private native static Class defineClass(String name, ClassLoader loader, int cookie);

可以看出BaseDexClassLoader中有个pathList对象，pathList中包含一个DexFile的集合dexElements，而对于类加载就是遍历这个集合，通过DexFile去寻找。

通俗点说，一个ClassLoader可以包含多个dex文件，每个dex文件是一个Element，多个dex文件排列成一个有序的数组dexElements，当找类的时候，会按顺序遍历dex文件，然后从当前遍历的dex文件中找类，如果找类则返回，如果找不到从下一个dex文件继续查找。那么这样的话，我们可以在这个数组的第一个元素放置我们的patch.jar，里面包含修复过的类，这样的话，当遍历findClass的时候，我们修复的类就会被查找到，从而替代有bug的类。

本片文章Tinker源码分析的两条线：

（1）应用启动时，从默认目录加载合并后的classes.dex

（2）patch下发后，合成classes.dex至目标目录

2．源码浅析

2.1  加载patch

加载的代码实际上在生成的Application中调用的，其父类为TinkerApplication，在其attachBaseContext中辗转会调用到loadTinker()方法，在该方法内部，反射调用了TinkerLoader的tryLoad方法。继而调用了tryLoadPatchFilesInternal方法。

@Override
public Intent tryLoad(TinkerApplication app, int tinkerFlag, boolean tinkerLoadVerifyFlag) {
    Intent resultIntent = new Intent();

    long begin = SystemClock.elapsedRealtime();
    tryLoadPatchFilesInternal(app, tinkerFlag, tinkerLoadVerifyFlag, resultIntent);
    long cost = SystemClock.elapsedRealtime() - begin;
    ShareIntentUtil.setIntentPatchCostTime(resultIntent, cost);
    return resultIntent;
}

private void tryLoadPatchFilesInternal(TinkerApplication app, int tinkerFlag, boolean tinkerLoadVerifyFlag, Intent resultIntent) {
    // 省略大量安全性校验代码

    if (isEnabledForDex) {
        //tinker/patch.info/patch-641e634c/dex
        boolean dexCheck = TinkerDexLoader.checkComplete(patchVersionDirectory, securityCheck, resultIntent);
        if (!dexCheck) {
            //file not found, do not load patch
            Log.w(TAG, "tryLoadPatchFiles:dex check fail");
            return;
        }
    }

    //now we can load patch jar
    if (isEnabledForDex) {
        boolean loadTinkerJars = TinkerDexLoader.loadTinkerJars(app, tinkerLoadVerifyFlag, patchVersionDirectory, resultIntent, isSystemOTA);
        if (!loadTinkerJars) {
            Log.w(TAG, "tryLoadPatchFiles:onPatchLoadDexesFail");
            return;
        }
    }
}

其中TinkerDexLoader.checkComplete主要是用于检查下发的meta文件中记录的dex信息（meta文件，可以查看生成patch的产物，在assets/dex-meta.txt），检查meta文件中记录的dex文件信息对应的dex文件是否存在，并把值存在TinkerDexLoader的静态变量dexList中。

TinkerDexLoader.loadTinkerJars传入四个参数，分别为application，tinkerLoadVerifyFlag（注解上声明的值，传入为false），patchVersionDirectory当前version的patch文件夹，intent，当前patch是否仅适用于art。

@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
public static boolean loadTinkerJars(Application application, boolean tinkerLoadVerifyFlag, 
    String directory, Intent intentResult, boolean isSystemOTA) {
        PathClassLoader classLoader = (PathClassLoader) TinkerDexLoader.class.getClassLoader();

        String dexPath = directory + "/" + DEX_PATH + "/";
        File optimizeDir = new File(directory + "/" + DEX_OPTIMIZE_PATH);

        ArrayList<File> legalFiles = new ArrayList<>();

        final boolean isArtPlatForm = ShareTinkerInternals.isVmArt();
        for (ShareDexDiffPatchInfo info : dexList) {
            //for dalvik, ignore art support dex
            if (isJustArtSupportDex(info)) {
                continue;
            }
            String path = dexPath + info.realName;
            File file = new File(path);

            legalFiles.add(file);
        }
        // just for art
        if (isSystemOTA) {
            parallelOTAResult = true;
            parallelOTAThrowable = null;
            Log.w(TAG, "systemOTA, try parallel oat dexes!!!!!");

            TinkerParallelDexOptimizer.optimizeAll(
                legalFiles, optimizeDir,
                new TinkerParallelDexOptimizer.ResultCallback() {
                }
            );

        SystemClassLoaderAdder.installDexes(application, classLoader, optimizeDir, legalFiles);
        return true;

找出仅支持art的dex，且当前patch是否仅适用于art时，并行去loadDex。关键是最后的installDexes：

@SuppressLint("NewApi")
public static void installDexes(Application application, PathClassLoader loader, File dexOptDir, List<File> files)
    throws Throwable {

    if (!files.isEmpty()) {
        ClassLoader classLoader = loader;
        if (Build.VERSION.SDK_INT >= 24) {
            classLoader = AndroidNClassLoader.inject(loader, application);
        }
        //because in dalvik, if inner class is not the same classloader with it wrapper class.
        //it won&#39;t fail at dex2opt
        if (Build.VERSION.SDK_INT >= 23) {
            V23.install(classLoader, files, dexOptDir);
        } else if (Build.VERSION.SDK_INT >= 19) {
            V19.install(classLoader, files, dexOptDir);
        } else if (Build.VERSION.SDK_INT >= 14) {
            V14.install(classLoader, files, dexOptDir);
        } else {
            V4.install(classLoader, files, dexOptDir);
        }
        //install done
        sPatchDexCount = files.size();
        Log.i(TAG, "after loaded classloader: " + classLoader + ", dex size:" + sPatchDexCount);

        if (!checkDexInstall(classLoader)) {
            //reset patch dex
            SystemClassLoaderAdder.uninstallPatchDex(classLoader);
            throw new TinkerRuntimeException(ShareConstants.CHECK_DEX_INSTALL_FAIL);
        }
    }
}

这里实际上就是根据不同的系统版本，去反射处理dexElements。我们看一下V19的实现：

private static final class V19 {
    private static void install(ClassLoader loader, List<File> additionalClassPathEntries,
                                File optimizedDirectory)
        throws IllegalArgumentException, IllegalAccessException,
        NoSuchFieldException, InvocationTargetException, NoSuchMethodException, IOException {

        Field pathListField = ShareReflectUtil.findField(loader, "pathList");
        Object dexPathList = pathListField.get(loader);
        ArrayList<IOException> suppressedExceptions = new ArrayList<IOException>();
        ShareReflectUtil.expandFieldArray(dexPathList, "dexElements", makeDexElements(dexPathList,
            new ArrayList<File>(additionalClassPathEntries), optimizedDirectory,
            suppressedExceptions));
        if (suppressedExceptions.size() > 0) {
            for (IOException e : suppressedExceptions) {
                Log.w(TAG, "Exception in makeDexElement", e);
                throw e;
            }
        }
    }
}

（1）找到PathClassLoader（BaseDexClassLoader）对象中的pathList对象

（2）根据pathList对象找到其中的makeDexElements方法，传入patch相关的对应的实参，返回Element[]对象

（3）拿到pathList对象中原本的dexElements方法

（4）步骤2与步骤3中的Element[]数组进行合并，将patch相关的dex放在数组的前面

（5）最后将合并后的数组，设置给pathList

2.2 合成patch

入口为onReceiveUpgradePatch()方法：

TinkerInstaller.onReceiveUpgradePatch(getApplicationContext(),
                Environment.getExternalStorageDirectory().getAbsolutePath() + "/patch_signed.apk");

上述代码会调用DefaultPatchListener中的onPatchReceived方法：

# DefaultPatchListener
@Override
public int onPatchReceived(String path) {

    int returnCode = patchCheck(path);

    if (returnCode == ShareConstants.ERROR_PATCH_OK) {
        TinkerPatchService.runPatchService(context, path);
    } else {
        Tinker.with(context).getLoadReporter().onLoadPatchListenerReceiveFail(new File(path), returnCode);
    }
    return returnCode;
}

首先对Tinker的相关配置（isEnable）以及patch的合法性进行检测，如果合法，则调用TinkerPatchService.runPatchService(context, path)。

public static void runPatchService(Context context, String path) {
    try {
        Intent intent = new Intent(context, TinkerPatchService.class);
        intent.putExtra(PATCH_PATH_EXTRA, path);
        intent.putExtra(RESULT_CLASS_EXTRA, resultServiceClass.getName());
        context.startService(intent);
    } catch (Throwable throwable) {
        TinkerLog.e(TAG, "start patch service fail, exception:" + throwable);
    }
}

TinkerPatchService是IntentService的子类，这里通过intent设置了两个参数，一个是patch的路径，一个是resultServiceClass，该值是调用Tinker.install的时候设置的，默认为DefaultTinkerResultService.class。由于是IntentService，直接看onHandleIntent即可。

@Override
protected void onHandleIntent(Intent intent) {
    final Context context = getApplicationContext();
    Tinker tinker = Tinker.with(context);
    String path = getPatchPathExtra(intent);
    File patchFile = new File(path);
    boolean result;
    increasingPriority();
    PatchResult patchResult = new PatchResult();
    result = upgradePatchProcessor.tryPatch(context, path, patchResult);
    patchResult.isSuccess = result;
    patchResult.rawPatchFilePath = path;
    patchResult.costTime = cost;
    patchResult.e = e;
    AbstractResultService.runResultService(context, patchResult, getPatchResultExtra(intent));
}

比较清晰，主要关注upgradePatchProcessor.tryPatch方法，调用的是UpgradePatch.tryPatch。这里有个有意思的地方increasingPriority()，其内部实现为：

private void increasingPriority() {
    TinkerLog.i(TAG, "try to increase patch process priority");
    try {
        Notification notification = new Notification();
        if (Build.VERSION.SDK_INT < 18) {
            startForeground(notificationId, notification);
        } else {
            startForeground(notificationId, notification);
            // start InnerService
            startService(new Intent(this, InnerService.class));
        }
    } catch (Throwable e) {
        TinkerLog.i(TAG, "try to increase patch process priority error:" + e);
    }
}

如果你对“保活”这个话题比较关注，那么对这段代码一定不陌生，主要是利用系统的一个漏洞来启动一个前台Service。下面继续回到tryPatch方法：

# UpgradePatch
@Override
public boolean tryPatch(Context context, String tempPatchPath, PatchResult patchResult) {
    Tinker manager = Tinker.with(context);

    final File patchFile = new File(tempPatchPath);

    //it is a new patch, so we should not find a exist
    SharePatchInfo oldInfo = manager.getTinkerLoadResultIfPresent().patchInfo;
    String patchMd5 = SharePatchFileUtil.getMD5(patchFile);

    //use md5 as version
    patchResult.patchVersion = patchMd5;
    SharePatchInfo newInfo;

    //already have patch
    if (oldInfo != null) {
        newInfo = new SharePatchInfo(oldInfo.oldVersion, patchMd5, Build.FINGERPRINT);
    } else {
        newInfo = new SharePatchInfo("", patchMd5, Build.FINGERPRINT);
    }

    //check ok, we can real recover a new patch
    final String patchDirectory = manager.getPatchDirectory().getAbsolutePath();
    final String patchName = SharePatchFileUtil.getPatchVersionDirectory(patchMd5);
    final String patchVersionDirectory = patchDirectory + "/" + patchName;

    //copy file
    File destPatchFile = new File(patchVersionDirectory + "/" + SharePatchFileUtil.getPatchVersionFile(patchMd5));
    // check md5 first
    if (!patchMd5.equals(SharePatchFileUtil.getMD5(destPatchFile))) {
        SharePatchFileUtil.copyFileUsingStream(patchFile, destPatchFile);
    }

 //we use destPatchFile instead of patchFile, because patchFile may be deleted during the patch process
    if (!DexDiffPatchInternal.tryRecoverDexFiles(manager, signatureCheck, context, patchVersionDirectory, 
                destPatchFile)) {
        TinkerLog.e(TAG, "UpgradePatch tryPatch:new patch recover, try patch dex failed");
        return false;
    }
    return true;
}

拷贝patch文件拷贝至私有目录，然后调用DexDiffPatchInternal.tryRecoverDexFiles：

protected static boolean tryRecoverDexFiles(Tinker manager, ShareSecurityCheck checker, Context context,
                                                
    String patchVersionDirectory, File patchFile) {
    String dexMeta = checker.getMetaContentMap().get(DEX_META_FILE);
    boolean result = patchDexExtractViaDexDiff(context, patchVersionDirectory, dexMeta, patchFile);
    return result;
}

直接看patchDexExtractViaDexDiff：

private static boolean patchDexExtractViaDexDiff(Context context, String patchVersionDirectory, String meta, final File patchFile) {
    String dir = patchVersionDirectory + "/" + DEX_PATH + "/";

    if (!extractDexDiffInternals(context, dir, meta, patchFile, TYPE_DEX)) {
        TinkerLog.w(TAG, "patch recover, extractDiffInternals fail");
        return false;
    }

    final Tinker manager = Tinker.with(context);

    File dexFiles = new File(dir);
    File[] files = dexFiles.listFiles();

    ...files遍历执行：DexFile.loadDex
     return true;
}

核心代码主要在extractDexDiffInternals中：

private static boolean extractDexDiffInternals(Context context, String dir, String meta, File patchFile, int type) {
    //parse meta
    ArrayList<ShareDexDiffPatchInfo> patchList = new ArrayList<>();
    ShareDexDiffPatchInfo.parseDexDiffPatchInfo(meta, patchList);

    File directory = new File(dir);
    //I think it is better to extract the raw files from apk
    Tinker manager = Tinker.with(context);
    ZipFile apk = null;
    ZipFile patch = null;

    ApplicationInfo applicationInfo = context.getApplicationInfo();

    String apkPath = applicationInfo.sourceDir; //base.apk
    apk = new ZipFile(apkPath);
    patch = new ZipFile(patchFile);

    for (ShareDexDiffPatchInfo info : patchList) {

        final String infoPath = info.path;
        String patchRealPath;
        if (infoPath.equals("")) {
            patchRealPath = info.rawName;
        } else {
            patchRealPath = info.path + "/" + info.rawName;
        }

        File extractedFile = new File(dir + info.realName);

        ZipEntry patchFileEntry = patch.getEntry(patchRealPath);
        ZipEntry rawApkFileEntry = apk.getEntry(patchRealPath);

        patchDexFile(apk, patch, rawApkFileEntry, patchFileEntry, info, extractedFile);
    }

    return true;
}

这里的代码比较关键了，可以看出首先解析了meta里面的信息，meta中包含了patch中每个dex的相关数据。然后通过Application拿到sourceDir，其实就是本机apk的路径以及patch文件；根据mate中的信息开始遍历，其实就是取出对应的dex文件，最后通过patchDexFile对两个dex文件做合并。

private static void patchDexFile(
            ZipFile baseApk, ZipFile patchPkg, ZipEntry oldDexEntry, ZipEntry patchFileEntry,
            ShareDexDiffPatchInfo patchInfo,  File patchedDexFile) throws IOException {
    InputStream oldDexStream = null;
    InputStream patchFileStream = null;

    oldDexStream = new BufferedInputStream(baseApk.getInputStream(oldDexEntry));
    patchFileStream = (patchFileEntry != null ? new BufferedInputStream(patchPkg.getInputStream(patchFileEntry)) : null);

    new DexPatchApplier(oldDexStream, patchFileStream).executeAndSaveTo(patchedDexFile);

}

通过ZipFile拿到其内部文件的InputStream，其实就是读取本地apk对应的dex文件，以及patch中对应dex文件，对二者的通过executeAndSaveTo方法进行合并至patchedDexFile，即patch的目标私有目录。至于合并算法，这里其实才是Tinker比较核心的地方，感兴趣可以参考这篇文章！

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