增量更新（客户端笔记）

一、概述

在上一篇文章我们了解了如何在服务端生成差分包，这篇文章我们主要来讲解客户端如何使用差分包进行合并

二、差分包的合并

1、首先创建jni目录并导入bspatch.c,并分析所需参数

#if 0
__FBSDID("$FreeBSD: src/usr.bin/bsdiff/bspatch/bspatch.c,v 1.1 2005/08/06 01:59:06 cperciva Exp $");
#endif

#include 
#include 
#include 
#include 
#include 
#include 



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 main(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   X
        16  8   Y
        24  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 bytes
    from oldfile to x bytes from the diff block; copy y bytes from the
    extra 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/* 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;i0];i++)
            if((oldpos+i>=0) && (oldpos+inew[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;
}

我们发现所需参数和生成差分包所需参数基本一致，并且我们需要导入bzip2，并在上述代码中进行引用

#include "bzip2/bzlib.c"
#include "bzip2/crctable.c"
#include "bzip2/compress.c"
#include "bzip2/decompress.c"
#include "bzip2/randtable.c"
#include "bzip2/blocksort.c"
#include "bzip2/huffman.c"
#include 
#include 
#include 
#include 
#include 
#include 

新建一个bsPatch.java如下，并生成头文件

public class BsPatch {

    /**
     * 
     * @param oldfile旧文件路径
     * @param newfile新文件路径
     * @param patchfile差分包
     */
    public native static void bsPatch(String oldfile, String newfile,
            String patchfile);

}

拷贝头文件到jni目录中，并在bspatch.c中引用，并调用其中的方法，如下

//合并
JNIEXPORT void JNICALL Java_com_saber_1bsdiff_BsPatch_bsPatch
  (JNIEnv *env, jclass jcls, jstring oldfile_jstr, jstring newfile_jstr, jstring patchfile_jstr){
    int argc = 4;
    char* oldfile = (char*)(*env)->GetStringUTFChars(env,oldfile_jstr, NULL);
    char* newfile = (char*)(*env)->GetStringUTFChars(env,newfile_jstr, NULL);
    char* patchfile = (char*)(*env)->GetStringUTFChars(env,patchfile_jstr, NULL);

    //参数（第一个参数无效）
    char *argv[4];
    argv[0] = "bspatch";
    argv[1] = oldfile;
    argv[2] = newfile;
    argv[3] = patchfile;

    bspathch_main(argc,argv);

    (*env)->ReleaseStringUTFChars(env,oldfile_jstr, oldfile);
    (*env)->ReleaseStringUTFChars(env,newfile_jstr, newfile);
    (*env)->ReleaseStringUTFChars(env,patchfile_jstr, patchfile);

}

然后builde project形成.so文件

在MainActivity中执行如下代码

class ApkUpdateTask extends AsyncTask<Void, Void, Boolean>{

        @Override
        protected Boolean doInBackground(Void... params) {
            try {
                //1.下载差分包
                File patchFile = DownloadUtils.download(Constants.URL_PATCH_DOWNLOAD);

                //获取当前应用的apk文件/data/app/app
                String oldfile = ApkUtils.getSourceApkPath(MainActivity.this, getPackageName());
                //2.合并得到最新版本的APK文件
                String newfile = Constants.NEW_APK_PATH;
                String patchfile = patchFile.getAbsolutePath();
                BsPatch.bsPatch(oldfile, newfile, patchfile);

            } catch (Exception e) {
                e.printStackTrace();
                return false;
            }

            return true;
        }

        @Override
        protected void onPostExecute(Boolean result) {
            super.onPostExecute(result);
            //3.安装
            if(result){

                ApkUtils.installApk(MainActivity.this, Constants.NEW_APK_PATH);
            }
        }

    }

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