Bsdiff and bspatch incremental updates

With Android ecology , Technology is becoming more and more mature , There is a lot of market at present Android It's a big project , The team is large , Gradually, many component-based plug-in technologies have been derived .

At the same time, because Android Installation package apk It's also growing , Every time I release , User update apk The environment is complex , If full update download apk In the case of using traffic , Bad network environment and so on , It's very bad for the user experience .

First, distinguish the following concepts

Componentization ： Put the common module code , extract lib Engineering or jar To achieve the effect of reuse .

pluggable ： The purpose is to extract the modules or functions that need to be implemented as an independent , Reduce the size of the host , When you need to use the corresponding function, load the corresponding module . It's about dynamic agents ,ClassLoader, And the other one apk Loading resources . for example ：360 Of DroidPlugin ( recommend )

Hot repair ： Often from repair bug From the angle of , It's important to fix the known... Without the need for a second install application bug( Key words involved ：Hook technology 、 Dynamic agents, etc ). for example ： Ali AndFix.

Incremental updating ：APK Incremental renewal is a lot of big factories APP Technology adopted .bsdiff The library generates patch files to download with the old version APK Synthesize to generate a new version APK Principle (ligbspatch.so). Mobile phone games app Incremental updates are used more . for example ：SmartAppUpdates

 bsdiff Generate patch -> bzip2 Compress -> android download patch -> bzip2 decompression patch -> bspatch Merge patch -> new apk

bsdiff It's not for apk Incremental update design , It can differentiate and merge any binary file .

bzip2 The function of Huffman is to compress the file losslessly ( Compress the differential packet for network transmission ) And decompress .

technological process ：

• On the server side , Generate two versions apk The difference subcontract of ;
• In the mobile client , Use the installed apk Synthesis with this differential package , Get a new version of apk;
• Verify the newly synthesized apk Is the document complete ,MD5 or SHA1 Whether it is right , If right , Then guide the user to install ;

Common commands

bsdiff Generate patch package command ：bsdiff oldfile newfile patchfile for example : bsdiff xx_v1.0.apk xx_v2.0.apk xx.patch

bspatch Generate a new APK： command ： bspatch oldfile newfile patchfile for example : bsdiff xx_v1.0.apk xx_v2.0.apk xx.patch

Use

Android Incremental updating ——bsdiff&bspatch

shortcoming ：

Incremental upgrade is not the perfect way to upgrade , There are at least two shortcomings ：

• Incremental upgrade is based on the difference between two application versions to generate patches , You can't guarantee users to upgrade to the latest in time every time , So you have to make a difference between each version you release and the latest version , So that all versions of users can differential upgrade , This operation is more cumbersome than the original package upgrade , However, it can be generated in batches through automated scripts .

• The prerequisite for a successful incremental upgrade is , The user's mobile terminal must have a version that allows you to copy it and is consistent with the version that your server uses for differential apk, So there is , for example , Built in system apk Can't get , No incremental upgrade ; For some versions consistent with your differential version , But the content has been modified ( For example, cracked version apk), In this way, incremental upgrade is not possible , To prevent compositing patch errors , Best to pass md5 Or in some other way patch Check the integrity of the package .