tinker有个非常大的亮点就是自研发了一套dex diff、patch相关算法。本篇文章主要目的就是分析该算法。当然值得注意的是,分析的前提就是需要对dex文件的格式要有一定的认识,否则的话可能会一脸懵逼态。

所以,本文会先对dex文件格式做一个简单的分析,也会做一些简单的实验,最后进入到dex diff,patch算法部分。

一、Dex文件格式浅析

首先简单了解下Dex文件,大家在反编译的时候,都清楚apk中会包含一个或者多个*.dex文件,该文件中存储了我们编写的代码,一般情况下我们还会通过工具转化为jar,然后通过一些工具反编译查看。

jar文件大家应该都清楚,类似于class文件的压缩包,一般情况下,我们直接解压就可以看到一个个class文件。而dex文件我们无法通过解压获取内部的一个个class文件,说明dex文件拥有自己特定的格式:
dex对Java类文件重新排列,将所有JAVA类文件中的常量池分解,消除其中的冗余信息,重新组合形成一个常量池,所有的类文件共享同一个常量池,使得相同的字符串、常量在DEX文件中只出现一次,从而减小了文件的体积。
接下来我们看看dex文件的内部结构到底是什么样子。

分析一个文件的组成,最好自己编写一个最简单的dex文件来分析。

(1)编写代码生成dex

首先我们编写一个类Hello.java:

public class Hello{
    public static void main(String[] args){
        System.out.println("hello dex!");
    }
}

然后进行编译:

javac -source 1.7 -target 1.7 Hello.java

最后通过dx工作将其转化为dex文件:

dx --dex --output=Hello.dex Hello.class

dx路径在Android-sdk/build-tools/版本号/dx下,如果无法识别dx命令,记得将该路径放到path下,或者使用绝对路径。
这样我们就得到了一个非常简单的dex文件。

(2)查看dex文件的内部结构

首先展示一张dex文件的大致的内部结构图:

Android 热修复 Tinker 源码分析之DexDiff / DexPatch

当然,单纯从一张图来说明肯定是远远不够的,因为我们后续要研究diff,patch算法,理论上我们应该要知道更多的细节,甚至要细致到:一个dex文件的每个字节表示的是什么内容。

对于一个类似于二进制的文件,最好的办法肯定不是靠记忆,好在有这么一个软件可以帮助我们的分析:

  • 软件名称:010 Editor

下载完成安装后,打开我们的dex文件,会引导你安装dex文件的解析模板。

最终打开效果图如下:

Android 热修复 Tinker 源码分析之DexDiff / DexPatch

上面部分代表了dex文件的内容(16进制的方式展示),下面部分展示了dex文件的各个区域,你可以通过点击下面部分,来查看其对应的内容区域以及内容。

当然这里也非常建议,阅读一些专门的文章来加深对dex文件的理解:

  • DEX文件格式分析
  • Android逆向之旅—解析编译之后的Dex文件格式

本文也仅会对dex文件做简单的格式分析。

(3)dex文件内部结构简单分析

dex_header
首先我们队dex_header做一个大致的分析,header中包含如下字段:

Android 热修复 Tinker 源码分析之DexDiff / DexPatch

首先我们猜测下header的作用,可以看到起包含了一些校验相关的字段,和整个dex文件大致区块的分布(off都为偏移量)。

这样的好处就是,当虚拟机读取dex文件时,只需要读取出header部分,就可以知道dex文件的大致区块分布了;并且可以检验出该文件格式是否正确、文件是否被篡改等。

  • 能够证明该文件是dex文件
  • checksum和signature主要用于校验文件的完整性
  • file_size为dex文件的大小
  • head_size为头文件的大小
  • endian_tag预设值为12345678,标识默认采用Little-Endian(自行搜索)。

剩下的几乎都是成对出现的size和off,大多代表各区块的包含的特定数据结构的数量和偏移量。例如:string_ids_off为112,指的是偏移量112开始为string_ids区域;string_ids_size为14,代表string_id_item的数量为14个。剩下的都类似就不介绍了。

结合010Editor可以看到各个区域包含的数据结构,以及对应的值,慢慢看就好了。

dex_map_list

除了header还有个比较重要的部分是dex_map_list,首先看个图:

Android 热修复 Tinker 源码分析之DexDiff / DexPatch

首先是map_item_list数量,接下来是每个map_item_list的描述。

map_item_list有什么用呢?

Android 热修复 Tinker 源码分析之DexDiff / DexPatch

可以看到每个map_list_item包含一个枚举类型,一个2字节暂未使用的成员、一个size表明当前类型的个数,offset表明当前类型偏移量。

拿本例来说:

  • 首先是TYPE_HEADER_ITEM类型,包含1个header(size=1),且偏移量为0。
  • 接下来是TYPE_STRING_ID_ITEM,包含14个string_id_item(size=14),且偏移量为112(如果有印象,header的长度为112,紧跟着header)。

剩下的依次类推~~

这样的话,可以看出通过map_list,可以将一个完整的dex文件划分成固定的区域(本例为13),且知道每个区域的开始,以及该区域对应的数据格式的个数。

通过map_list找到各个区域的开始,每个区域都会对应特定的数据结构,通过010 Editor看就好了。

二、分析前的思考

现在我们了解了dex的基本格式,接下来我们考虑下如何做dex diff 和 patch。

先要考虑的是我们有什么:

  1. old dex
  2. new dex

我们想要生成一个patch文件,该文件和old dex 通过patch算法还能生成new dex。

  • 那么我们该如何做呢?

根据上文的分析,我们知道dex文件大致有3个部分(这里3个部分主要用于分析,勿较真):

  1. header
  2. 各个区域
  3. map list

header实际上是可以根据后面的数据确定其内容的,并且是定长112的;各个区域后面说;map list实际上可以做到定位到各个区域开始位置;

我们最终patch + old dex -> new dex;针对上述的3个部分,

  • header我们可以不做处理,因为可以根据其他数据生成;
  • map list这个东西,其实我们主要要的是各个区域的开始(offset)
  • 知道了各个区域的offset后,在我们生成new dex的时候,我们就可以定位各个区域的开始和结束位置,那么只需要往各个区域写数据即可。

那么我们看看针对一个区域的diff,假设有个string区域,主要用于存储字符串:

old dex该区域的字符串有: Hello、World、zhy
new dex该区域的字符串有: Android、World、zhy

可以看出,针对该区域,我们删除了Hello,增加了Android。

那么patch中针对该区域可以如下记录:
“del Hello , add Android”(实际情况需要转化为二进制)。

想想应用中可以直接读取出old dex,即知道:

  • 原来该区域包含:Hello、World、zhy
  • patch中该区域包含:”del Hello , add Android”

那么,可以非常容易的计算出new dex中包含:

Android、World、zhy。

这样我们就完成了一个区域大致的diff和patch算法,其他各个区域的diff和patch和上述类似。

这样来看,是不是觉得这个diff和patch算法也没有那么的复杂,实际上tinker的做法与上述类似,实际情况可能要比上述描述要复杂一些,但是大体上是差不多的。

有了一个大致的算法概念之后,我们就可以去看源码了。

三、Tinker DexDiff源码浅析

这里看代码实际上也是有技巧的,tinker的代码实际上蛮多的,往往你可以会陷在一堆的代码中。我们可以这么考虑,比如diff算法,输入参数为old dex 、new dex,输出为patch file。

那么肯定存在某个类,或者某个方法接受和输出上述参数。实际上该类为DexPatchGenerator:

diff的API使用代码为:

@Test
public void testDiff() throws IOException {
    File oldFile = new File("Hello.dex");
    File newFile = new File("Hello-World.dex");

    File patchFile = new File("patch.dex");
    DexPatchGenerator dexPatchGenerator
            = new DexPatchGenerator(oldFile, newFile);
    dexPatchGenerator.executeAndSaveTo(patchFile);
}

代码在tinker-build的tinker-patch-lib下。

写一个单元测试或者main方法,上述几行代码就是diff算法。

所以查看代码时要有针对性,比如看diff算法,就找到diff算法的入口,不要在gradle plugin中去纠结。

(1)dex file => Dex
public DexPatchGenerator(File oldDexFile, File newDexFile) throws IOException {
    this(new Dex(oldDexFile), new Dex(newDexFile));
}

将我们传入的dex文件转化为了Dex对象。

public Dex(File file) throws IOException {
    // 删除了一堆代码
    InputStream  in = new BufferedInputStream(new FileInputStream(file));
    loadFrom(in, (int) file.length());     
}

private void loadFrom(InputStream in, int initSize) throws IOException {
    byte[] rawData = FileUtils.readStream(in, initSize);
    this.data = ByteBuffer.wrap(rawData);
    this.data.order(ByteOrder.LITTLE_ENDIAN);
    this.tableOfContents.readFrom(this);
}

首先将我们的文件读取为byte[]数组(这里还是蛮耗费内存的),然后由ByteBuffer进行包装,并设置字节顺序为小端(这里说明ByteBuffer还是蛮方便的。然后通过readFrom方法为Dex对象的tableOfContents赋值。

#TableOfContents
public void readFrom(Dex dex) throws IOException {
    readHeader(dex.openSection(header));
    // special case, since mapList.byteCount is available only after
    // computeSizesFromOffsets() was invoked, so here we can't use
    // dex.openSection(mapList) to get dex section. Or
    // an {@code java.nio.BufferUnderflowException} will be thrown.
    readMap(dex.openSection(mapList.off));
    computeSizesFromOffsets();
}

在其内部执行了readHeader和readMap,上文我们大致分析了header和map list相关,实际上就是将这两个区域转化为一定的数据结构,读取然后存储到内存中。

首先看readHeader:

private void readHeader(Dex.Section headerIn) throws UnsupportedEncodingException {
    byte[] magic = headerIn.readByteArray(8);
    int apiTarget = DexFormat.magicToApi(magic);

    if (apiTarget != DexFormat.API_NO_EXTENDED_OPCODES) {
        throw new DexException("Unexpected magic: " + Arrays.toString(magic));
    }

    checksum = headerIn.readInt();
    signature = headerIn.readByteArray(20);
    fileSize = headerIn.readInt();
    int headerSize = headerIn.readInt();
    if (headerSize != SizeOf.HEADER_ITEM) {
        throw new DexException("Unexpected header: 0x" + Integer.toHexString(headerSize));
    }
    int endianTag = headerIn.readInt();
    if (endianTag != DexFormat.ENDIAN_TAG) {
        throw new DexException("Unexpected endian tag: 0x" + Integer.toHexString(endianTag));
    }
    linkSize = headerIn.readInt();
    linkOff = headerIn.readInt();
    mapList.off = headerIn.readInt();
    if (mapList.off == 0) {
        throw new DexException("Cannot merge dex files that do not contain a map");
    }
    stringIds.size = headerIn.readInt();
    stringIds.off = headerIn.readInt();
    typeIds.size = headerIn.readInt();
    typeIds.off = headerIn.readInt();
    protoIds.size = headerIn.readInt();
    protoIds.off = headerIn.readInt();
    fieldIds.size = headerIn.readInt();
    fieldIds.off = headerIn.readInt();
    methodIds.size = headerIn.readInt();
    methodIds.off = headerIn.readInt();
    classDefs.size = headerIn.readInt();
    classDefs.off = headerIn.readInt();
    dataSize = headerIn.readInt();
    dataOff = headerIn.readInt();
}

如果你现在打开着010 Editor,或者看一眼最前面的图,实际上就是将header中所有的字段定义出来,读取响应的字节并赋值。

接下来看readMap:

private void readMap(Dex.Section in) throws IOException {
    int mapSize = in.readInt();
    Section previous = null;
    for (int i = 0; i < mapSize; i++) {
        short type = in.readShort();
        in.readShort(); // unused
        Section section = getSection(type);
        int size = in.readInt();
        int offset = in.readInt();

        section.size = size;
        section.off = offset;

        previous = section;
    }

    header.off = 0;

    Arrays.sort(sections);

    // Skip header section, since its offset must be zero.
    for (int i = 1; i < sections.length; ++i) {
        if (sections[i].off == Section.UNDEF_OFFSET) {
            sections[i].off = sections[i - 1].off;
        }
    }
}

这里注意,在读取header的时候,实际上已经读取除了map list区域的offset,并存储在mapList.off中。所以map list中实际上是从这个位置开始的。首先读取的就是map_list_item的个数,接下来读取的就是每个map_list_item对应的实际数据。

可以看到依次读取:type,unused,size,offset,如果你还有印象前面我们描述了map_list_item是与此对应的,对应的数据结构为TableContents.Section对象。

computeSizesFromOffsets()主要为section的byteCount(占据了多个字节)参数赋值。

到这里就完成了dex file 到 Dex对象的初始化。

有了两个Dex对象之后,就需要去做diff操作了。

(2)dex diff

继续回到源码:

public DexPatchGenerator(File oldDexFile, InputStream newDexStream) throws IOException {
    this(new Dex(oldDexFile), new Dex(newDexStream));
}

直接到两个Dex对象的构造函数:

public DexPatchGenerator(Dex oldDex, Dex newDex) {
    this.oldDex = oldDex;
    this.newDex = newDex;

    SparseIndexMap oldToNewIndexMap = new SparseIndexMap();
    SparseIndexMap oldToPatchedIndexMap = new SparseIndexMap();
    SparseIndexMap newToPatchedIndexMap = new SparseIndexMap();
    SparseIndexMap selfIndexMapForSkip = new SparseIndexMap();

    additionalRemovingClassPatternSet = new HashSet<>();

    this.stringDataSectionDiffAlg = new StringDataSectionDiffAlgorithm(
            oldDex, newDex,
            oldToNewIndexMap,
            oldToPatchedIndexMap,
            newToPatchedIndexMap,
            selfIndexMapForSkip
    );
    this.typeIdSectionDiffAlg = ...
    this.protoIdSectionDiffAlg = ...
    this.fieldIdSectionDiffAlg = ...
    this.methodIdSectionDiffAlg = ...
    this.classDefSectionDiffAlg = ...
    this.typeListSectionDiffAlg = ...
    this.annotationSetRefListSectionDiffAlg = ... 
    this.annotationSetSectionDiffAlg = ...
    this.classDataSectionDiffAlg = ... 
    this.codeSectionDiffAlg = ...
    this.debugInfoSectionDiffAlg = ...
    this.annotationSectionDiffAlg = ...
    this.encodedArraySectionDiffAlg = ...
    this.annotationsDirectorySectionDiffAlg = ...
}

看到其首先为oldDex,newDex赋值,然后依次初始化了15个算法,每个算法代表每个区域,算法的目的就像我们之前描述的那样,要知道“删除了哪些,新增了哪些”;

我们继续看代码:

dexPatchGenerator.executeAndSaveTo(patchFile);

有了dexPatchGenerator对象后,直接指向了executeAndSaveTo方法。

public void executeAndSaveTo(File file) throws IOException {
    OutputStream os = null;
    try {
        os = new BufferedOutputStream(new FileOutputStream(file));
        executeAndSaveTo(os);
    } finally {
        if (os != null) {
            try {
                os.close();
            } catch (Exception e) {
                // ignored.
            }
        }
    }
}

到executeAndSaveTo方法:

public void executeAndSaveTo(OutputStream out) throws IOException {
    int patchedheaderSize = SizeOf.HEADER_ITEM;
    int patchedStringIdsSize = newDex.getTableOfContents().stringIds.size * SizeOf.STRING_ID_ITEM;
    int patchedTypeIdsSize = newDex.getTableOfContents().typeIds.size * SizeOf.TYPE_ID_ITEM;

    int patchedProtoIdsSize = newDex.getTableOfContents().protoIds.size * SizeOf.PROTO_ID_ITEM;

    int patchedFieldIdsSize = newDex.getTableOfContents().fieldIds.size * SizeOf.MEMBER_ID_ITEM;
    int patchedMethodIdsSize = newDex.getTableOfContents().methodIds.size * SizeOf.MEMBER_ID_ITEM;
    int patchedClassDefsSize = newDex.getTableOfContents().classDefs.size * SizeOf.CLASS_DEF_ITEM;

    int patchedIdSectionSize =
            patchedStringIdsSize
                    + patchedTypeIdsSize
                    + patchedProtoIdsSize
                    + patchedFieldIdsSize
                    + patchedMethodIdsSize
                    + patchedClassDefsSize;

    this.patchedHeaderOffset = 0;

    this.patchedStringIdsOffset = patchedHeaderOffset + patchedheaderSize;

    this.stringDataSectionDiffAlg.execute();
    this.patchedStringDataItemsOffset = patchedheaderSize + patchedIdSectionSize;

    this.stringDataSectionDiffAlg.simulatePatchOperation(this.patchedStringDataItemsOffset);

    // 省略了其余14个算法的一堆代码
    this.patchedDexSize
            = this.patchedMapListOffset
            + patchedMapListSize;
    writeResultToStream(out);
}

因为涉及到15个算法,所以这里的代码非常长,我们这里只拿其中一个算法来说明。

每个算法都会执行execute和simulatePatchOperation方法:

首先看execute:

public void execute() {
    this.patchOperationList.clear();

    // 1. 拿到oldDex和newDex的itemList
    this.adjustedOldIndexedItemsWithOrigOrder = collectSectionItems(this.oldDex, true);
    this.oldItemCount = this.adjustedOldIndexedItemsWithOrigOrder.length;

    AbstractMap.SimpleEntry<Integer, T>[] adjustedOldIndexedItems = new AbstractMap.SimpleEntry[this.oldItemCount];
    System.arraycopy(this.adjustedOldIndexedItemsWithOrigOrder, 0, adjustedOldIndexedItems, 0, this.oldItemCount);
    Arrays.sort(adjustedOldIndexedItems, this.comparatorForItemDiff);

    AbstractMap.SimpleEntry<Integer, T>[] adjustedNewIndexedItems = collectSectionItems(this.newDex, false);
    this.newItemCount = adjustedNewIndexedItems.length;
    Arrays.sort(adjustedNewIndexedItems, this.comparatorForItemDiff);

    int oldCursor = 0;
    int newCursor = 0;
    // 2.遍历,对比,收集patch操作
    while (oldCursor < this.oldItemCount || newCursor < this.newItemCount) {
        if (oldCursor >= this.oldItemCount) {
            // rest item are all newItem.
            while (newCursor < this.newItemCount) {
                // 对剩下的newItem做ADD操作
            }
        } else if (newCursor >= newItemCount) {
            // rest item are all oldItem.
            while (oldCursor < oldItemCount) {
                // 对剩下的oldItem做DEL操作
            }
        } else {
            AbstractMap.SimpleEntry<Integer, T> oldIndexedItem = adjustedOldIndexedItems[oldCursor];
            AbstractMap.SimpleEntry<Integer, T> newIndexedItem = adjustedNewIndexedItems[newCursor];
            int cmpRes = oldIndexedItem.getValue().compareTo(newIndexedItem.getValue());
            if (cmpRes < 0) {
                int deletedIndex = oldIndexedItem.getKey();
                int deletedOffset = getItemOffsetOrIndex(deletedIndex, oldIndexedItem.getValue());
                this.patchOperationList.add(new PatchOperation<T>(PatchOperation.OP_DEL, deletedIndex));
                markDeletedIndexOrOffset(this.oldToPatchedIndexMap, deletedIndex, deletedOffset);
                ++oldCursor;
            } else if (cmpRes > 0) {
                this.patchOperationList.add(new PatchOperation<>(PatchOperation.OP_ADD,
                        newIndexedItem.getKey(), newIndexedItem.getValue()));
                ++newCursor;
            } else {
                int oldIndex = oldIndexedItem.getKey();
                int newIndex = newIndexedItem.getKey();
                int oldOffset = getItemOffsetOrIndex(oldIndexedItem.getKey(), oldIndexedItem.getValue());
                int newOffset = getItemOffsetOrIndex(newIndexedItem.getKey(), newIndexedItem.getValue());

                if (oldIndex != newIndex) {
                    this.oldIndexToNewIndexMap.put(oldIndex, newIndex);
                }

                if (oldOffset != newOffset) {
                    this.oldOffsetToNewOffsetMap.put(oldOffset, newOffset);
                }

                ++oldCursor;
                ++newCursor;
            }
        }
    }

    // 未完
}

可以看到首先读取oldDex和newDex对应区域的数据并排序,分别adjustedOldIndexedItems和adjustedNewIndexedItems。

接下来就开始遍历了,直接看else部分:

分别根据当前的cursor,获取oldItem和newItem,对其value对对比:

  • 如果<0 ,则认为该old Item被删除了,记录为PatchOperation.OP_DEL,并记录该oldItem index到PatchOperation对象,加入到patchOperationList中。
  • 如果>0,则认为该newItem是新增的,记录为PatchOperation.OP_ADD,并记录该newItem index和value到PatchOperation对象,加入到patchOperationList中。
  • 如果=0,不会生成PatchOperation。

经过上述,我们得到了一个patchOperationList对象。

继续下半部分代码:

public void execute() {
    // 接上...

    // 根据index排序,如果index一样,则先DEL后ADD
    Collections.sort(this.patchOperationList, comparatorForPatchOperationOpt);

    Iterator<PatchOperation<T>> patchOperationIt = this.patchOperationList.iterator();
    PatchOperation<T> prevPatchOperation = null;
    while (patchOperationIt.hasNext()) {
        PatchOperation<T> patchOperation = patchOperationIt.next();
        if (prevPatchOperation != null
                && prevPatchOperation.op == PatchOperation.OP_DEL
                && patchOperation.op == PatchOperation.OP_ADD
                ) {
            if (prevPatchOperation.index == patchOperation.index) {
                prevPatchOperation.op = PatchOperation.OP_REPLACE;
                prevPatchOperation.newItem = patchOperation.newItem;
                patchOperationIt.remove();
                prevPatchOperation = null;
            } else {
                prevPatchOperation = patchOperation;
            }
        } else {
            prevPatchOperation = patchOperation;
        }
    }

    // Finally we record some information for the final calculations.
    patchOperationIt = this.patchOperationList.iterator();
    while (patchOperationIt.hasNext()) {
        PatchOperation<T> patchOperation = patchOperationIt.next();
        switch (patchOperation.op) {
            case PatchOperation.OP_DEL: {
                indexToDelOperationMap.put(patchOperation.index, patchOperation);
                break;
            }
            case PatchOperation.OP_ADD: {
                indexToAddOperationMap.put(patchOperation.index, patchOperation);
                break;
            }
            case PatchOperation.OP_REPLACE: {
                indexToReplaceOperationMap.put(patchOperation.index, patchOperation);
                break;
            }
        }
    }
}
  1. 首先对patchOperationList按照index排序,如果index一致则先DEL、后ADD。
  2. 接下来一个对所有的operation的迭代,主要将index一致的,且连续的DEL、ADD转化为REPLACE操作。
  3. 最后将patchOperationList转化为3个Map,分别为:indexToDelOperationMap,indexToAddOperationMap,indexToReplaceOperationMap。

ok,经历完成execute之后,我们主要的产物就是3个Map,分别记录了:oldDex中哪些index需要删除;newDex中新增了哪些item;哪些item需要替换为新item。

刚才说了每个算法除了execute()还有个simulatePatchOperation()

this.stringDataSectionDiffAlg
    .simulatePatchOperation(this.patchedStringDataItemsOffset);

传入的偏移量为data区域的偏移量。

public void simulatePatchOperation(int baseOffset) {
    int oldIndex = 0;
    int patchedIndex = 0;
    int patchedOffset = baseOffset;
    while (oldIndex < this.oldItemCount || patchedIndex < this.newItemCount) {
        if (this.indexToAddOperationMap.containsKey(patchedIndex)) {
            //省略了一些代码
            T newItem = patchOperation.newItem;
            int itemSize = getItemSize(newItem);
            ++patchedIndex;
            patchedOffset += itemSize;
        } else if (this.indexToReplaceOperationMap.containsKey(patchedIndex)) {
            //省略了一些代码
            T newItem = patchOperation.newItem;
            int itemSize = getItemSize(newItem);
            ++patchedIndex;
            patchedOffset += itemSize;
        } else if (this.indexToDelOperationMap.containsKey(oldIndex)) {
            ++oldIndex;
        } else if (this.indexToReplaceOperationMap.containsKey(oldIndex)) {
            ++oldIndex;
        } else if (oldIndex < this.oldItemCount) {
            ++oldIndex;
            ++patchedIndex;
            patchedOffset += itemSize;
        }
    }

    this.patchedSectionSize = SizeOf.roundToTimesOfFour(patchedOffset - baseOffset);
}

遍历oldIndex与newIndex,分别在indexToAddOperationMap,indexToReplaceOperationMap,indexToDelOperationMap中查找。

这里关注一点最终的一个产物是this.patchedSectionSize,由patchedOffset-baseOffset所得。
这里有几种情况会造成patchedOffset+=itemSize:

  1. indexToAddOperationMap中包含patchIndex
  2. indexToReplaceOperationMap包含patchIndex
  3. 不在indexToDelOperationMap与indexToReplaceOperationMap中的oldDex.

其实很好理解,这个patchedSectionSize其实对应newDex的这个区域的size。所以,包含需要ADD的Item,会被替代的Item,以及OLD ITEMS中没有被删除和替代的Item。这三者相加即为newDex的itemList。

到这里,一个算法就执行完毕了。

经过这样的一个算法,我们得到了PatchOperationList和对应区域sectionSize。那么执行完成所有的算法,应该会得到针对每个算法的PatchOperationList,和每个区域的sectionSize;每个区域的sectionSize实际上换算得到每个区域的offset。

每个区域的算法,execute和simulatePatchOperation代码都是复用的,所以其他的都只有细微的变化,可以自己看了。

接下来看执行完成所有的算法后的writeResultToStream方法。

(3) 生成patch文件
private void writeResultToStream(OutputStream os) throws IOException {
    DexDataBuffer buffer = new DexDataBuffer();
    buffer.write(DexPatchFile.MAGIC); // DEXDIFF
    buffer.writeShort(DexPatchFile.CURRENT_VERSION); /0x0002
    buffer.writeInt(this.patchedDexSize);
    // we will return here to write firstChunkOffset later.
    int posOfFirstChunkOffsetField = buffer.position();
    buffer.writeInt(0);
    buffer.writeInt(this.patchedStringIdsOffset);
    buffer.writeInt(this.patchedTypeIdsOffset);
    buffer.writeInt(this.patchedProtoIdsOffset);
    buffer.writeInt(this.patchedFieldIdsOffset);
    buffer.writeInt(this.patchedMethodIdsOffset);
    buffer.writeInt(this.patchedClassDefsOffset);
    buffer.writeInt(this.patchedMapListOffset);
    buffer.writeInt(this.patchedTypeListsOffset);
    buffer.writeInt(this.patchedAnnotationSetRefListItemsOffset);
    buffer.writeInt(this.patchedAnnotationSetItemsOffset);
    buffer.writeInt(this.patchedClassDataItemsOffset);
    buffer.writeInt(this.patchedCodeItemsOffset);
    buffer.writeInt(this.patchedStringDataItemsOffset);
    buffer.writeInt(this.patchedDebugInfoItemsOffset);
    buffer.writeInt(this.patchedAnnotationItemsOffset);
    buffer.writeInt(this.patchedEncodedArrayItemsOffset);
    buffer.writeInt(this.patchedAnnotationsDirectoryItemsOffset);
    buffer.write(this.oldDex.computeSignature(false));
    int firstChunkOffset = buffer.position();
    buffer.position(posOfFirstChunkOffsetField);
    buffer.writeInt(firstChunkOffset);
    buffer.position(firstChunkOffset);

    writePatchOperations(buffer, this.stringDataSectionDiffAlg.getPatchOperationList());
    // 省略其他14个writePatch...

    byte[] bufferData = buffer.array();
    os.write(bufferData);
    os.flush();
}
  • 首先写了MAGIC,CURRENT_VERSION主要用于检查该文件为合法的tinker patch 文件。
  • 然后写入patchedDexSize
  • 第四位写入的是数据区的offset,可以看到先使用0站位,等所有的map list相关的offset书写结束,写入当前的位置。
  • 接下来写入所有的跟maplist各个区域相关的offset(这里各个区域的排序不重要,读写一致即可)
  • 然后执行每个算法写入对应区域的信息
  • 最后生成patch文件

我们依旧只看stringDataSectionDiffAlg这个算法。

private <T extends Comparable<T>> void writePatchOperations(
        DexDataBuffer buffer, List<PatchOperation<T>> patchOperationList
) {
    List<Integer> delOpIndexList = new ArrayList<>(patchOperationList.size());
    List<Integer> addOpIndexList = new ArrayList<>(patchOperationList.size());
    List<Integer> replaceOpIndexList = new ArrayList<>(patchOperationList.size());

    List<T> newItemList = new ArrayList<>(patchOperationList.size());

    for (PatchOperation<T> patchOperation : patchOperationList) {
        switch (patchOperation.op) {
            case PatchOperation.OP_DEL: {
                delOpIndexList.add(patchOperation.index);
                break;
            }
            case PatchOperation.OP_ADD: {
                addOpIndexList.add(patchOperation.index);
                newItemList.add(patchOperation.newItem);
                break;
            }
            case PatchOperation.OP_REPLACE: {
                replaceOpIndexList.add(patchOperation.index);
                newItemList.add(patchOperation.newItem);
                break;
            }
        }
    }

    buffer.writeUleb128(delOpIndexList.size());
    int lastIndex = 0;
    for (Integer index : delOpIndexList) {
        buffer.writeSleb128(index - lastIndex);
        lastIndex = index;
    }

    buffer.writeUleb128(addOpIndexList.size());
    lastIndex = 0;
    for (Integer index : addOpIndexList) {
        buffer.writeSleb128(index - lastIndex);
        lastIndex = index;
    }

    buffer.writeUleb128(replaceOpIndexList.size());
    lastIndex = 0;
    for (Integer index : replaceOpIndexList) {
        buffer.writeSleb128(index - lastIndex);
        lastIndex = index;
    }

    for (T newItem : newItemList) {
        if (newItem instanceof StringData) {
            buffer.writeStringData((StringData) newItem);
        } 
        // else 其他类型,write其他类型Data

    }
}

首先将我们的patchOperationList转化为3个OpIndexList,分别对应DEL,ADD,REPLACE,以及将所有的item存入newItemList。

然后依次写入:

  1. del操作的个数,每个del的index
  2. add操作的个数,每个add的index
  3. replace操作的个数,每个需要replace的index
  4. 最后依次写入newItemList.

这里index都做了(这里做了个index – lastIndex操作)

其他的算法也是执行了类似的操作。

最好来看看我们生成的patch是什么样子的:

  1. 首先包含几个字段,证明自己是tinker patch
  2. 包含生成newDex各个区域的offset,即可以将newDex划分了多个区域,定位到起点
  3. 包含newDex各个区域的Item的删除的索引(oldDex),新增的索引和值,替换的索引和值

那么这么看,我们猜测Patch的逻辑时这样的:

  1. 首先根据各个区域的offset,确定各个区域的起点
  2. 读取oldDex各个区域的items,然后根据patch中去除掉oldDex中需要删除的和需要替换的item,再加上新增的item和替换的item即可组成newOld该区域的items。

即,newDex的某个区域的包含:

oldItems - del - replace + addItems + replaceItems

这么看挺清晰的,下面看代码咯~

四、Tinker DexPatch源码浅析
(1)寻找入口

与diff一样,肯定有那么一个类或者方法,接受old dex File 和 patch File,最后生成new Dex。不要陷在一堆安全校验,apk解压的代码中。

这个类叫做DexPatchApplier,在tinker-commons中。

patch的相关代码如下:

@Test
public void testPatch() throws IOException {
    File oldFile = new File("Hello.dex");
    File patchFile = new File("patch.dex");

    File newFile = new File("new.dex");

    DexPatchApplier dexPatchGenerator
            = new DexPatchApplier(oldFile, patchFile);
    dexPatchGenerator.executeAndSaveTo(newFile);
}

可以看到和diff代码类似,下面看代码去。

(2)源码分析
public DexPatchApplier(File oldDexIn, File patchFileIn) throws IOException {
    this(new Dex(oldDexIn), new DexPatchFile(patchFileIn));
}

oldDex会转化为Dex对象,这个上面分析过,主要就是readHeader和readMap.注意我们的patchFile是转为一个DexPatchFile对象。

public DexPatchFile(File file) throws IOException {
    this.buffer = new DexDataBuffer(ByteBuffer.wrap(FileUtils.readFile(file)));
    init();
}

首先将patch file读取为byte[],然后调用init

private void init() {
    byte[] magic = this.buffer.readByteArray(MAGIC.length);
    if (CompareUtils.uArrCompare(magic, MAGIC) != 0) {
        throw new IllegalStateException("bad dex patch file magic: " + Arrays.toString(magic));
    }

    this.version = this.buffer.readShort();
    if (CompareUtils.uCompare(this.version, CURRENT_VERSION) != 0) {
        throw new IllegalStateException("bad dex patch file version: " + this.version + ", expected: " + CURRENT_VERSION);
    }

    this.patchedDexSize = this.buffer.readInt();
    this.firstChunkOffset = this.buffer.readInt();
    this.patchedStringIdSectionOffset = this.buffer.readInt();
    this.patchedTypeIdSectionOffset = this.buffer.readInt();
    this.patchedProtoIdSectionOffset = this.buffer.readInt();
    this.patchedFieldIdSectionOffset = this.buffer.readInt();
    this.patchedMethodIdSectionOffset = this.buffer.readInt();
    this.patchedClassDefSectionOffset = this.buffer.readInt();
    this.patchedMapListSectionOffset = this.buffer.readInt();
    this.patchedTypeListSectionOffset = this.buffer.readInt();
    this.patchedAnnotationSetRefListSectionOffset = this.buffer.readInt();
    this.patchedAnnotationSetSectionOffset = this.buffer.readInt();
    this.patchedClassDataSectionOffset = this.buffer.readInt();
    this.patchedCodeSectionOffset = this.buffer.readInt();
    this.patchedStringDataSectionOffset = this.buffer.readInt();
    this.patchedDebugInfoSectionOffset = this.buffer.readInt();
    this.patchedAnnotationSectionOffset = this.buffer.readInt();
    this.patchedEncodedArraySectionOffset = this.buffer.readInt();
    this.patchedAnnotationsDirectorySectionOffset = this.buffer.readInt();
    this.oldDexSignature = this.buffer.readByteArray(SizeOf.SIGNATURE);

    this.buffer.position(firstChunkOffset);
}

还记得我们写patch的操作么,先写了MAGIC和Version用于校验该文件是一个patch file;接下来为patchedDexSize和各种offset进行赋值;最后定位到数据区(firstChunkOffset),还记得写的时候,该字段在第四个位置。

定位到该位置后,后面读取的就是数据了,数据存的时候按照如下格式存储的:

  1. del操作的个数,每个del的index
  2. add操作的个数,每个add的index
  3. replace操作的个数,每个需要replace的index
  4. 最后依次写入newItemList.

简单回忆下,我们继续源码分析。

public DexPatchApplier(File oldDexIn, File patchFileIn) throws IOException {
    this(new Dex(oldDexIn), new DexPatchFile(patchFileIn));
}

public DexPatchApplier(
        Dex oldDexIn,
        DexPatchFile patchFileIn) {
    this.oldDex = oldDexIn;
    this.patchFile = patchFileIn;
    this.patchedDex = new Dex(patchFileIn.getPatchedDexSize());
    this.oldToPatchedIndexMap = new SparseIndexMap();
}

除了oldDex,patchFile,还初始化了一个patchedDex作为我们最终输出Dex对象。

构造完成后,直接执行了executeAndSaveTo方法。

public void executeAndSaveTo(File file) throws IOException {
    OutputStream os = null;
    try {
        os = new BufferedOutputStream(new FileOutputStream(file));
        executeAndSaveTo(os);
    } finally {
        if (os != null) {
            try {
                os.close();
            } catch (Exception e) {
                // ignored.
            }
        }
    }
}

直接到executeAndSaveTo(os),该方法代码比较长,我们分3段讲解:

public void executeAndSaveTo(OutputStream out) throws IOException {

    TableOfContents patchedToc = this.patchedDex.getTableOfContents();

    patchedToc.header.off = 0;
    patchedToc.header.size = 1;
    patchedToc.mapList.size = 1;

    patchedToc.stringIds.off
            = this.patchFile.getPatchedStringIdSectionOffset();
    patchedToc.typeIds.off
            = this.patchFile.getPatchedTypeIdSectionOffset();
    patchedToc.typeLists.off
            = this.patchFile.getPatchedTypeListSectionOffset();
    patchedToc.protoIds.off
            = this.patchFile.getPatchedProtoIdSectionOffset();
    patchedToc.fieldIds.off
            = this.patchFile.getPatchedFieldIdSectionOffset();
    patchedToc.methodIds.off
            = this.patchFile.getPatchedMethodIdSectionOffset();
    patchedToc.classDefs.off
            = this.patchFile.getPatchedClassDefSectionOffset();
    patchedToc.mapList.off
            = this.patchFile.getPatchedMapListSectionOffset();
    patchedToc.stringDatas.off
            = this.patchFile.getPatchedStringDataSectionOffset();
    patchedToc.annotations.off
            = this.patchFile.getPatchedAnnotationSectionOffset();
    patchedToc.annotationSets.off
            = this.patchFile.getPatchedAnnotationSetSectionOffset();
    patchedToc.annotationSetRefLists.off
            = this.patchFile.getPatchedAnnotationSetRefListSectionOffset();
    patchedToc.annotationsDirectories.off
            = this.patchFile.getPatchedAnnotationsDirectorySectionOffset();
    patchedToc.encodedArrays.off
            = this.patchFile.getPatchedEncodedArraySectionOffset();
    patchedToc.debugInfos.off
            = this.patchFile.getPatchedDebugInfoSectionOffset();
    patchedToc.codes.off
            = this.patchFile.getPatchedCodeSectionOffset();
    patchedToc.classDatas.off
            = this.patchFile.getPatchedClassDataSectionOffset();
    patchedToc.fileSize
            = this.patchFile.getPatchedDexSize();

    Arrays.sort(patchedToc.sections);

    patchedToc.computeSizesFromOffsets();

    // 未完待续...

}

这里实际上,就是读取patchFile中记录的值给patchedDex的TableOfContent中各种Section(大致对应map list中各个map_list_item)赋值。

接下来排序呢,设置byteCount等字段信息。

继续:

public void executeAndSaveTo(OutputStream out) throws IOException {

    // 省略第一部分代码

    // Secondly, run patch algorithms according to sections' dependencies.
    this.stringDataSectionPatchAlg = new StringDataSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.typeIdSectionPatchAlg = new TypeIdSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.protoIdSectionPatchAlg = new ProtoIdSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.fieldIdSectionPatchAlg = new FieldIdSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.methodIdSectionPatchAlg = new MethodIdSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.classDefSectionPatchAlg = new ClassDefSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.typeListSectionPatchAlg = new TypeListSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.annotationSetRefListSectionPatchAlg = new AnnotationSetRefListSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.annotationSetSectionPatchAlg = new AnnotationSetSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.classDataSectionPatchAlg = new ClassDataSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.codeSectionPatchAlg = new CodeSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.debugInfoSectionPatchAlg = new DebugInfoItemSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.annotationSectionPatchAlg = new AnnotationSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.encodedArraySectionPatchAlg = new StaticValueSectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );
    this.annotationsDirectorySectionPatchAlg = new AnnotationsDirectorySectionPatchAlgorithm(
            patchFile, oldDex, patchedDex, oldToPatchedIndexMap
    );

    this.stringDataSectionPatchAlg.execute();
    this.typeIdSectionPatchAlg.execute();
    this.typeListSectionPatchAlg.execute();
    this.protoIdSectionPatchAlg.execute();
    this.fieldIdSectionPatchAlg.execute();
    this.methodIdSectionPatchAlg.execute();
    this.annotationSectionPatchAlg.execute();
    this.annotationSetSectionPatchAlg.execute();
    this.annotationSetRefListSectionPatchAlg.execute();
    this.annotationsDirectorySectionPatchAlg.execute();
    this.debugInfoSectionPatchAlg.execute();
    this.codeSectionPatchAlg.execute();
    this.classDataSectionPatchAlg.execute();
    this.encodedArraySectionPatchAlg.execute();
    this.classDefSectionPatchAlg.execute();

    //未完待续...

}

这一部分很明显初始化了一堆算法,然后分别去执行。我们依然是拿stringDataSectionPatchAlg来分析。

public void execute() {
    final int deletedItemCount = patchFile.getBuffer().readUleb128();
    final int[] deletedIndices = readDeltaIndiciesOrOffsets(deletedItemCount);

    final int addedItemCount = patchFile.getBuffer().readUleb128();
    final int[] addedIndices = readDeltaIndiciesOrOffsets(addedItemCount);

    final int replacedItemCount = patchFile.getBuffer().readUleb128();
    final int[] replacedIndices = readDeltaIndiciesOrOffsets(replacedItemCount);

    final TableOfContents.Section tocSec = getTocSection(this.oldDex);
    Dex.Section oldSection = null;

    int oldItemCount = 0;
    if (tocSec.exists()) {
        oldSection = this.oldDex.openSection(tocSec);
        oldItemCount = tocSec.size;
    }

    // Now rest data are added and replaced items arranged in the order of
    // added indices and replaced indices.
    doFullPatch(
            oldSection, oldItemCount, deletedIndices, addedIndices, replacedIndices
    );
}

再贴一下我们写入时的规则:

  1. del操作的个数,每个del的index
  2. add操作的个数,每个add的index
  3. replace操作的个数,每个需要replace的index
  4. 最后依次写入newItemList.

看代码,读取顺序如下:

  1. del的数量,del的所有的index存储在一个int[]中;
  2. add的数量,add的所有的index存储在一个int[]中;
  3. replace的数量,replace的所有的index存储在一个int[]中;

是不是和写入时一致。

继续,接下来获取了oldDex中oldItems和oldItemCount。

那么现在有了:

  1. del count and indices
  2. add count add indices
  3. replace count and indices
  4. oldItems and oldItemCount

拿着我们拥有的,继续执行doFullPatch

private void doFullPatch(
        Dex.Section oldSection,
        int oldItemCount,
        int[] deletedIndices,
        int[] addedIndices,
        int[] replacedIndices) {
    int deletedItemCount = deletedIndices.length;
    int addedItemCount = addedIndices.length;
    int replacedItemCount = replacedIndices.length;
    int newItemCount = oldItemCount + addedItemCount - deletedItemCount;

    int deletedItemCounter = 0;
    int addActionCursor = 0;
    int replaceActionCursor = 0;

    int oldIndex = 0;
    int patchedIndex = 0;

    while (oldIndex < oldItemCount || patchedIndex < newItemCount) {
        if (addActionCursor < addedItemCount && addedIndices[addActionCursor] == patchedIndex) {
            T addedItem = nextItem(patchFile.getBuffer());
            int patchedOffset = writePatchedItem(addedItem);
            ++addActionCursor;
            ++patchedIndex;
        } else
        if (replaceActionCursor < replacedItemCount && replacedIndices[replaceActionCursor] == patchedIndex) {
            T replacedItem = nextItem(patchFile.getBuffer());
            int patchedOffset = writePatchedItem(replacedItem);
            ++replaceActionCursor;
            ++patchedIndex;
        } else
        if (Arrays.binarySearch(deletedIndices, oldIndex) >= 0) {
            T skippedOldItem = nextItem(oldSection); // skip old item.

            ++oldIndex;
            ++deletedItemCounter;
        } else
        if (Arrays.binarySearch(replacedIndices, oldIndex) >= 0) {
            T skippedOldItem = nextItem(oldSection); // skip old item.

            ++oldIndex;
        } else
        if (oldIndex < oldItemCount) {
            T oldItem = adjustItem(this.oldToPatchedIndexMap, nextItem(oldSection));

            int patchedOffset = writePatchedItem(oldItem);

            ++oldIndex;
            ++patchedIndex;
        }
    }
}

先整体上看一下,这里的目的就是往patchedDex的stringData区写数据,写的数据理论上应该是:

  1. 新增的数据
  2. 替代的数据
  3. oldDex中出去新增和被替代的数据

当然他们需要顺序写入。

所以看代码,首先计算出newItemCount=oldItemCount + addCount - delCount,然后开始遍历,遍历条件为0~oldItemCount或0~newItemCount。

我们期望的是,在patchIndex从0~newItemCount之间都会写入对应的Item。

Item写入通过代码我们可以看到:

  1. 首先判断该patchIndex是否包含在addIndices中,如果包含则写入;
  2. 再者判断是否在repalceIndices中,如果包含则写入;
  3. 然后判断如果发现oldIndex被delete或者replace,直接跳过;
  4. 那么最后一个index指的就是,oldIndex为非delete和replace的,也就是和newDex中items相同的部分。

上述1.2.4三个部分即可组成完整的newDex的该区域。

这样的话就完成了stringData区域的patch算法。

其他剩下的14个算法的execute代码是相同的(父类),执行的操作类似,都会完成各个部分的patch算法。

当所有的区域都完成恢复后,那么剩下的就是header和mapList了,所以回到所有算法执行完成的地方:

public void executeAndSaveTo(OutputStream out) throws IOException {

    //1.省略了offset的各种赋值
    //2.省略了各个部分的patch算法

    // Thirdly, write header, mapList. Calculate and write patched dex's sign and checksum.
    Dex.Section headerOut = this.patchedDex.openSection(patchedToc.header.off);
    patchedToc.writeHeader(headerOut);

    Dex.Section mapListOut = this.patchedDex.openSection(patchedToc.mapList.off);
    patchedToc.writeMap(mapListOut);

    this.patchedDex.writeHashes();

    // Finally, write patched dex to file.
    this.patchedDex.writeTo(out);
}

定位到header区域,写header相关数据;定位到map list区域,编写map list相关数据。两者都完成的时候,需要编写header中比较特殊的两个字段:签名和checkSum,因为这两个字段是依赖map list的,所以必须在编写map list后。

这样就完成了完整的dex的恢复,最后将内存中的所有数据写到文件中。

五、案例简单分析
(1)dex准备

刚才我们有个Hello.dex,我们再编写一个类:

public class World{
    public static void main(String[] args){
        System.out.println("nani World");
    }
}

然后将这个类编译以及打成dx文件。

javac -source 1.7 -target 1.7 World.java
dx --dex --output=World.dex World.class

这样我们就准备好了两个dex,Hello.dex和World.dex.

(2) diff

使用010 Editor分别打开两个dex,我们主要关注string_id_item;

Android 热修复 Tinker 源码分析之DexDiff / DexPatch

两边分别13个字符串,按照我们上面介绍的diff算法,我们可以得到以下操作:

两边的字符串分别开始遍历对比:

  • 如果<0 ,则认为该old Item被删除了,记录为PatchOperation.OP_DEL,并记录该oldItem index到PatchOperation对象,加入到patchOperationList中。
  • 如果>0,则认为该newItem是新增的,记录为PatchOperation.OP_ADD,并记录该newItem index和value到PatchOperation对象,加入到patchOperationList中。
  • 如果=0,不会生成PatchOperation。
del 1
add 1 LWorld; 
del 2
add 8 World.java
del 10
add 11 naniWorld

然后是根据索引排序,没有变化;

接下来遍历所有的操作,将index一致且DEL和ADD相邻的操作替换为replace

replace 1 LWorld
del 2
add 8 World.java
del 10
add 11 naniWorld

最终在write时,会做一次遍历,将操作按DEL,ADD,REPLACE进行分类,并且将出现的item放置到newItemList中。

del ops:
    del 2
    del 10
add ops:
    add 8
    add 11
replace ops:
    replace 1

newItemList变为:

LWorld //replace 1 
World.java //add 8 
naniWorld //add 11

然后写入,那么写入的顺序应该是:

2 //del size
2 
8 // index - lastIndex
2 // add size
8
3 // index - lastIndex
1 //replace size
1
LWorld
World.java
naniWorld

这里我们直接在DexPatchGenerator的writeResultToStream的相关位置打上日志:

buffer.writeUleb128(delOpIndexList.size());
System.out.println("del size = " + delOpIndexList.size());
int lastIndex = 0;
for (Integer index : delOpIndexList) {
    buffer.writeSleb128(index - lastIndex);
    System.out.println("del index = " + (index - lastIndex));
    lastIndex = index;
}
buffer.writeUleb128(addOpIndexList.size());
System.out.println("add size = " + addOpIndexList.size());
lastIndex = 0;
for (Integer index : addOpIndexList) {
    buffer.writeSleb128(index - lastIndex);
    System.out.println("add index = " + (index - lastIndex));
    lastIndex = index;
}
buffer.writeUleb128(replaceOpIndexList.size());
System.out.println("replace size = " + addOpIndexList.size());
lastIndex = 0;
for (Integer index : replaceOpIndexList) {
    buffer.writeSleb128(index - lastIndex);
    System.out.println("replace index = " + (index - lastIndex));

    lastIndex = index;
}

for (T newItem : newItemList) {
    if (newItem instanceof StringData) {
        buffer.writeStringData((StringData) newItem);
        System.out.println("stringdata  = " + ((StringData) newItem).value);
      }
}

可以看到输出为:

del size = 2
del index = 2
del index = 8
add size = 2
add index = 8
add index = 3
replace size = 2
replace index = 1
stringdata  = LWorld;
stringdata  = World.java
stringdata  = nani World

与我们上述分析结果一致 ~~

那么其他区域可以用类似的方式去验证,patch的话也差不多,就不赘述了。

原文来自:http://www.codeceo.com/article/tinker-source-code-analysis-dexdiff-dexpatch.html

本文地址:https://www.linuxprobe.com/android-tinker-dexdiff.html编辑员:郭建鹏,审核员:逄增宝

本文原创地址:https://www.linuxprobe.com/android-tinker-dexdiff.html编辑:roc_guo,审核员:暂无