Android更新优化 - 增量更新是如何节省用户时间和流量的

增量更新和全量更新

我想玩过大型手游的人都知道，手游的安装包非常大，因为资源图片众多。而你每次更新都把所有文件都更新下来，是非常耗时的，对吧。耗时是一个方面，有些人在户外开的是移动网络，动不动就几个G。这对于用户来说，是一笔不小的浪费。那么就引入了我们今天的话题，增量更新。

说起增量更新，那么就不得不提及一下与它相对的概念，全量更新。全量更新，是大多数，乃至几乎所有app的更新方式，即把整个安装包都下载下来。那既然大家都用全量更新，那必定有其存在的合理之处，存在即合理，对吧。全量更新流程非常简洁，而增量更新流程相对比较复杂，且一般应用的安装包不是很大，使用增量更新就像高射炮打苍蝇，这是一个方面，也是主要的方面。还有一个方面是因为，增量更新有一定的门槛，需要有一定的NDK和C语言的基础。

增量更新的流程（服务端）

增量更新无需下载最新的完整版本的apk文件，而只需下载本地版本升到最新版本的补丁文件，然后使用本地正在运行的app的merge补丁的功能合并成一个完整的最新版本的apk文件，最后手动将这个合并好的apk文件安装。

安装包1.1版本 = 安装包1.0版本 merge 1.0版本升1.1版本的补丁文件

1.0版本升1.1版本的补丁文件 = 安装包1.1版本 diff 安装包1.0版本

我们补丁拆分的过程是后端完成的，而补丁合并的过程是Android端完成的。后端需要使用云服务器下载一个类似于bsdiff-4.3.tar.gz的压缩包，然后解压并使用其命令进行补丁文件的拆分。

wget https://src.fedoraproject.org/lookaside/pkgs/bsdiff/bsdiff-4.3.tar.gz/e6d812394f0e0ecc8d5df255aa1db22a/bsdiff-4.3.tar.gz
tar zxvf bsdiff-4.3.tar.gz
cd bsdiff-4.3

~~然后编译，运行，结束~~。

你以为事情会有如此顺利？

vim Makefile

截屏2023-07-18 18.41.51.png
注意看.ifndef WITHOUT_MAN这一行和.endif这一行，输入i进入insert模式，光标移动到这两行最前面，按下tab键缩进下格式，然后esc，退出insert模式到命令模式，输入冒号“:”，最后输入wq!回车保存退出。

截屏2023-07-18 18.46.37.png
最后make进行编译。

make

截屏2023-07-18 18.48.14.png
这样我们就得到了两个绿色的可执行文件。

bsdiff [oldfile] [newfile] [patchfile]

最后我们就可以正常执行文件拆分命令了。比如我们电脑本地的文件上传。

sftp root@dorachat.com

先使用sftp登录服务器，root@后面改成你服务器的公网ip，不要跟我的一样，你登不上来。

put old_apk_1.0.apk
put new_apk_1.1.apk

bsdiff命令的使用格式是这样。

bsdiff [oldfile] [newfile] [patchfile]

那我们就执行。

./bsdiff old_apk_1.0.apk new_apk_1.1.apk patch_1.0_1.1.patch

执行完成就会在当前目录生成patch_1.0_1.1.patch补丁文件了，这个路径要根据你apk实际存在服务器的路径，要不然也是没法读取的。最后将补丁文件的下载地址通过接口返回给客户端，服务端的事情就做完了。

增量更新的流程（Android端）

Android端要使用到NDK，所以，你得先确保安装好了NDK和CMake的包。

截屏2023-07-18 18.59.45.png

截屏2023-07-18 19.00.42.png

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然后写一个PatchUtils工具类。

package com.dorachat.dorachat.util;public class PatchUtils {public native static int mergePatch(String oldApkPath, String newApkPath, String patchPath);static {System.loadLibrary("patchUpdate");}
}

截屏2023-07-18 19.03.38.png
然后将这些bzip相关的c文件扔进cpp文件夹，再修改app模块的build.gradle.kts，也可能是build.gradle，看你用的什么构建脚本了。

android {splits {abi {isEnable = truereset()include("x86", "x86_64", "armeabi-v7a", "arm64-v8a")// select ABIs to build APKs forisUniversalApk = true// generate an additional APK that contains all the ABIs}}externalNativeBuild {cmake {path = file("src/main/cpp/CMakeLists.txt")version = "3.18.1"}}
}

CMakeLists.txt的写法。


# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html# Sets the minimum version of CMake required to build the native library.cmake_minimum_required(VERSION 3.18.1)# Declares and names the project.project("app")# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.find_library( # Sets the name of the path variable.log-liblog)# 不要加，跟增量更新没有关系
add_library(cryptoMsgSHAREDRSAUtils.hRSAUtils.cpp)
# 指定要编译成动态库的c文件
add_library(patchUpdateSHAREDbspatch.cbzip2/blocksort.cbzip2/bzip2.cbzip2/bzip2recover.cbzip2/bzlib.cbzip2/compress.cbzip2/crctable.cbzip2/decompress.cbzip2/dlltest.cbzip2/huffman.cbzip2/mk251.cbzip2/randtable.cbzip2/spewG.cbzip2/unzcrash.c
)#include_directories(src/main/cpp/bzip2)#set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")#include_directories(src/main/cpp/)
# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.target_link_libraries( # Specifies the target library.#   cryptoMsgpatchUpdate${log-lib})

命令的入口代码bspatch.c。

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <jni.h>
#include <err.h>
#include <string.h>
#include "bzip2/bzlib.h"static off_t offtin(u_char *buf) {off_t y;y = buf[7] & 0x7F;y = y * 256;y += buf[6];y = y * 256;y += buf[5];y = y * 256;y += buf[4];y = y * 256;y += buf[3];y = y * 256;y += buf[2];y = y * 256;y += buf[1];y = y * 256;y += buf[0];if (buf[7] & 0x80) y = -y;return y;
}int patchMethod(int argc, char *argv[]) {FILE *f, *cpf, *dpf, *epf;BZFILE *cpfbz2, *dpfbz2, *epfbz2;int cbz2err, dbz2err, ebz2err;int fd;ssize_t oldsize, newsize;ssize_t bzctrllen, bzdatalen;u_char header[32], buf[8];u_char *old, *new;off_t oldpos, newpos;off_t ctrl[3];off_t lenread;off_t i;if (argc != 4) errx(1, "usage: %s oldfile newfile patchfile\n", argv[0]);/* Open patch file */if ((f = fopen(argv[3], "r")) == NULL)err(1, "fopen(%s)", argv[3]);/*File format:0  8  "BSDIFF40"8  8  X16 8  Y24 8  sizeof(newfile)32 X  bzip2(control block)32+X   Y  bzip2(diff block)32+X+Y ???    bzip2(extra block)with control block a set of triples (x,y,z) meaning "add x bytesfrom oldfile to x bytes from the diff block; copy y bytes from theextra block; seek forwards in oldfile by z bytes".*//* Read header */if (fread(header, 1, 32, f) < 32) {if (feof(f))errx(1, "Corrupt patch\n");err(1, "fread(%s)", argv[3]);}/* Check for appropriate magic */if (memcmp(header, "BSDIFF40", 8) != 0)errx(1, "Corrupt patch\n");/* Read lengths from header */bzctrllen = offtin(header + 8);bzdatalen = offtin(header + 16);newsize = offtin(header + 24);if ((bzctrllen < 0) || (bzdatalen < 0) || (newsize < 0))errx(1, "Corrupt patch\n");/* Close patch file and re-open it via libbzip2 at the right places */if (fclose(f))err(1, "fclose(%s)", argv[3]);if ((cpf = fopen(argv[3], "r")) == NULL)err(1, "fopen(%s)", argv[3]);if (fseeko(cpf, 32, SEEK_SET))err(1, "fseeko(%s, %lld)", argv[3],(long long) 32);if ((cpfbz2 = BZ2_bzReadOpen(&cbz2err, cpf, 0, 0, NULL, 0)) == NULL)errx(1, "BZ2_bzReadOpen, bz2err = %d", cbz2err);if ((dpf = fopen(argv[3], "r")) == NULL)err(1, "fopen(%s)", argv[3]);if (fseeko(dpf, 32 + bzctrllen, SEEK_SET))err(1, "fseeko(%s, %lld)", argv[3],(long long) (32 + bzctrllen));if ((dpfbz2 = BZ2_bzReadOpen(&dbz2err, dpf, 0, 0, NULL, 0)) == NULL)errx(1, "BZ2_bzReadOpen, bz2err = %d", dbz2err);if ((epf = fopen(argv[3], "r")) == NULL)err(1, "fopen(%s)", argv[3]);if (fseeko(epf, 32 + bzctrllen + bzdatalen, SEEK_SET))err(1, "fseeko(%s, %lld)", argv[3],(long long) (32 + bzctrllen + bzdatalen));if ((epfbz2 = BZ2_bzReadOpen(&ebz2err, epf, 0, 0, NULL, 0)) == NULL)errx(1, "BZ2_bzReadOpen, bz2err = %d", ebz2err);if (((fd = open(argv[1], O_RDONLY, 0)) < 0) ||((oldsize = lseek(fd, 0, SEEK_END)) == -1) ||((old = malloc(oldsize + 1)) == NULL) ||(lseek(fd, 0, SEEK_SET) != 0) ||(read(fd, old, oldsize) != oldsize) ||(close(fd) == -1))err(1, "%s", argv[1]);if ((new = malloc(newsize + 1)) == NULL) err(1, NULL);oldpos = 0;newpos = 0;while (newpos < newsize) {/* Read control data */for (i = 0; i <= 2; i++) {lenread = BZ2_bzRead(&cbz2err, cpfbz2, buf, 8);if ((lenread < 8) || ((cbz2err != BZ_OK) &&(cbz2err != BZ_STREAM_END)))errx(1, "Corrupt patch\n");ctrl[i] = offtin(buf);};/* Sanity-check */if (newpos + ctrl[0] > newsize)errx(1, "Corrupt patch\n");/* Read diff string */lenread = BZ2_bzRead(&dbz2err, dpfbz2, new + newpos, ctrl[0]);if ((lenread < ctrl[0]) ||((dbz2err != BZ_OK) && (dbz2err != BZ_STREAM_END)))errx(1, "Corrupt patch\n");/* Add old data to diff string */for (i = 0; i < ctrl[0]; i++)if ((oldpos + i >= 0) && (oldpos + i < oldsize))new[newpos + i] += old[oldpos + i];/* Adjust pointers */newpos += ctrl[0];oldpos += ctrl[0];/* Sanity-check */if (newpos + ctrl[1] > newsize)errx(1, "Corrupt patch\n");/* Read extra string */lenread = BZ2_bzRead(&ebz2err, epfbz2, new + newpos, ctrl[1]);if ((lenread < ctrl[1]) ||((ebz2err != BZ_OK) && (ebz2err != BZ_STREAM_END)))errx(1, "Corrupt patch\n");/* Adjust pointers */newpos += ctrl[1];oldpos += ctrl[2];};/* Clean up the bzip2 reads */BZ2_bzReadClose(&cbz2err, cpfbz2);BZ2_bzReadClose(&dbz2err, dpfbz2);BZ2_bzReadClose(&ebz2err, epfbz2);if (fclose(cpf) || fclose(dpf) || fclose(epf))err(1, "fclose(%s)", argv[3]);/* Write the new file */if (((fd = open(argv[2], O_CREAT | O_TRUNC | O_WRONLY, 0666)) < 0) ||(write(fd, new, newsize) != newsize) || (close(fd) == -1))err(1, "%s", argv[2]);free(new);free(old);return 0;
}JNIEXPORT jint JNICALL Java_com_dorachat_dorachat_util_PatchUtils_mergePatch(JNIEnv *env, jclass cls,jstring old_apk_path, jstring new_apk_path, jstring patch_path) {int argc = 4;char *argv[argc];argv[0] = "bspatch";argv[1] = (char *) ((*env)->GetStringUTFChars(env, old_apk_path, 0));argv[2] = (char *) ((*env)->GetStringUTFChars(env, new_apk_path, 0));argv[3] = (char *) ((*env)->GetStringUTFChars(env, patch_path, 0));int ret = patchMethod(argc, argv);(*env)->ReleaseStringUTFChars(env, old_apk_path, argv[1]);(*env)->ReleaseStringUTFChars(env, new_apk_path, argv[2]);(*env)->ReleaseStringUTFChars(env, patch_path, argv[3]);return ret;
}

bzip2的源文件，网上很多。比如这个
https://github.com/hongyangAndroid/BsDiff_And_Patch 。
提取本地apk文件可以使用这个方法。

    public static File extractApk(Context context) {ApplicationInfo applicationInfo = context.getApplicationContext().getApplicationInfo();String apkPath = applicationInfo.sourceDir;File apkFile = new File(apkPath);return apkFile;}

或者你直接使用
https://github.com/dora4/dora/blob/master/dora-mvvm/src/main/java/dora/util/ApkUtils.java 。

说到最后

最后聊一聊更新的具体逻辑。增量更新有固定数量法和固定业务法。你可以规定，相差版本小于等于3个，就采用增量更新，大于3个，直接走全量更新。此为固定数量法。固定业务法则是，版本分为大小版本号的更新，每个大版本必须走全量更新，而大版本中的小版本则采用增量更新。大版本采用强制更新，而小版本则可采用选择更新。每次更新到大版本，可能会再次拉取该版本的最终小版本的补丁文件发起二次更新。