Use apktool, aapt2, bundletool to convert apk to aab (Android App Bundle)

Scenarios encountered in development

In the previous article, we talked about the summary of the use of the AAPT2 command line. There is a usage scenario in which is to convert the apk to an aab file. The aab file is the specified package format for the application on Google Play. Let’s practice it below.
If we have such a scenario requirement, a game or application is connected to the aggregation SDK we developed, and then provides us with an apk package. We can use the packaging tool to integrate the specific channel SDK or plug-in with this apk package. Now we need This package is released overseas, so only the aab package will be released.
We first print out the integrated apk package through the packaging tool, and then further process the apk

Tools used in practice

apktool, a tool for decompiling and compiling apk, download address: Apktool - A tool for reverse engineering 3rd party, closed, binary Android apps.
bundletool, a command-line tool for building app bundles and SDK Bundles by yourself, download address: Releases · google/bundletool · GitHub
aapt2, is a build tool that parses resources, indexes resources, and compiles resources into a binary format optimized for the Android platform, in the installed SDK directory android_sdk/build-tools/version/下找到aapt2，也可以最新的版本，比如下载3.2.0-alpha18-4804415版本，其他版本替换地址里面的版本就可以了: https://dl.google.com/dl/android /maven2/com/android/tools/build/aapt2/8.0.0-alpha07-9193536/aapt2-8.0.0-alpha07-9193536-windows.jar
android.jar, the SDK development kit provided by android, can be found under android_sdk/platforms/ /version
jarsigner, a signature tool, under the installed JDK bin directory, the jdk environment variable is configured to run the command line directly
Please install JDK and configure environment variables to facilitate the execution of commands in the cmd window

Implemented using the command line

First choose a directory, copy the downloaded apktool, aapt2, bundletool, android.jar and other tools to this directory, so that we can execute commands, and prepare a packaged apk to change the directory, such as my newly created directory D:\ workspace\LCQ\apk-aab:
Next, we enter cmd in the file address bar and press Enter to enter the cmd command interface
Use the apktool command to decompile the app-release.apk package and execute the command
```
java -jar apktool_2.6.1.jar d app-release.apk -s -o decode_apk
```
We focus on the res folder after decompilation. The resource files in res need to be compiled with aapt2 to generate files that meet Google's protocol buffer format requirements.
We use the compile command of aapt2 to compile the res folder
```
aapt2 compile --dir decode_apk\res -o compiled_resources.zip
```
You can see that the generated zip archive contains binary files with the suffix .flat or arsc.flat
We then use the link command of aapt2 to generate a base.apk
```
aapt2 link --proto-format -o base.apk -I android.jar --manifest decode_apk\AndroidManifest.xml -R compiled_resources.zip --auto-add-overlay
```
We decompress the base.apk file, create a new manifest folder, move the AndroidManifest.xml file into it, and then copy the assets and lib in the directory (decode_apk) generated by apktool decompilation to base, and add the .dex suffix Copy all the files to module/dex, copy unknown and kotlin to module/root, and the final directory will look like this

Then we select all the files and directories under the module and compress them into a .zip file, as shown in the figure

Please make sure that the base directory is not compressed after the compressed zip file is opened, we copy the compressed base.zip to the same directory as bundletool,

When we copy, we must pay attention not to mistake the directory generated by decompilation and the decompressed base directory resource generated by aapt2 link, otherwise the bundletool command will fail, such as InvalidProtocolBufferException

[BT:1.12.1] Error: com.google.protobuf.InvalidProtocolBufferException: Protocol message end-group tag did not match expected tag.
java.io.UncheckedIOException: com.google.protobuf.InvalidProtocolBufferException: Protocol message end-group tag did not match expected tag.
        at com.android.tools.build.bundletool.model.BundleModule$Builder.addEntry(BundleModule.java:418)
        at com.android.tools.build.bundletool.model.BundleModule$Builder.addEntries(BundleModule.java:399)
        at com.android.tools.build.bundletool.model.utils.BundleModuleParser.parseBundleModuleInternal(BundleModuleParser.java:66)
        at com.android.tools.build.bundletool.model.utils.BundleModuleParser.parseAppBundleModule(BundleModuleParser.java:41)
        at com.android.tools.build.bundletool.validation.BundleModulesValidator.lambda$validate$0(BundleModulesValidator.java:75)
        at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
        at java.base/java.util.Collections$2.tryAdvance(Collections.java:4747)
        at java.base/java.util.Collections$2.forEachRemaining(Collections.java:4755)
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
        at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
        at com.android.tools.build.bundletool.validation.BundleModulesValidator.validate(BundleModulesValidator.java:76)
        at com.android.tools.build.bundletool.commands.BuildBundleCommand.execute(BuildBundleCommand.java:231)
        at com.android.tools.build.bundletool.BundleToolMain.main(BundleToolMain.java:78)
        at com.android.tools.build.bundletool.BundleToolMain.main(BundleToolMain.java:54)
Caused by: com.google.protobuf.InvalidProtocolBufferException: Protocol message end-group tag did not match expected tag.
        at com.google.protobuf.InvalidProtocolBufferException.invalidEndTag(InvalidProtocolBufferException.java:129)
        at com.google.protobuf.CodedInputStream$StreamDecoder.checkLastTagWas(CodedInputStream.java:2124)
        at com.google.protobuf.AbstractParser.parsePartialFrom(AbstractParser.java:217)
        at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:232)
        at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:237)
        at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:48)
        at com.google.protobuf.GeneratedMessageV3.parseWithIOException(GeneratedMessageV3.java:339)
        at com.android.aapt.Resources$XmlNode.parseFrom(Resources.java:44493)
        at com.android.tools.build.bundletool.model.BundleModule$SpecialModuleEntry$1.addToModule(BundleModule.java:459)
        at com.android.tools.build.bundletool.model.BundleModule$Builder.addEntry(BundleModule.java:416)
        ... 16 more

Next we use the bundletool command to generate the aab file, execute the command
```
java -jar bundletool-all-1.12.1.jar build-bundle --modules=base.zip --output=module.aab
```
You can see that the aab file has been generated. Now it is impossible to use the bundletool tool to directly install and test it, because it has not been signed yet. The aab signature can only be signed by jarsigner, not apksigner

Use the jarsigner command to sign base.aab

jarsigner -digestalg SHA1 -sigalg SHA1withRSA -keystore 你的签名文件.jks -storepass 秘钥文件密码 -keypass 秘钥密码 base.aab 别名

You can see that the signature is successful, and the META-INF directory is generated, which contains the signature information file

The signed base.aab file can be used to test and upload google play
If you want to test the aab file, you also need to use the command line of bundletool. Let us first let adb connect to the device and generate the device information json file
```
java -jar bundletool-all-1.12.1.jar get-device-spec --output=./device-spec.json
```

Then generate apks

java -jar bundletool-all-1.12.1.jar build-apks --bundle=base.aab --output=abase.apks --overwrite --ks=你的签名文件.jks --ks-pass=pass:"111111" --ks-key-alias=别名--key-pass=pass:"111111"

Then install the apks to the corresponding device

ava -jar bundletool-all-1.12.1.jar install-apks --apks=base.apks

Tip: Since we use the apk to generate aab by ourselves, there may be file omissions in the middle processing process, special cases that have not been processed, etc. It must be that the aab generated by AS is more reliable, and it is recommended to use the aab generated by AS to put your own on the shelf application