RN差量更新

目前常见的diff工具有bsdiff和google-diff-match-patch。
google-diff-match-patch可以参考这篇文章。
这里我是想用bsdiff来实现，主要的思路：

• 在上传时，服务器使用bsdiff算法将老RN包和新RN包生成一个补丁patch文件，供客户端下载。（这步服务器不好做，可以我们生成好上传）
• 用户下载patch文件，使用bspatch算法将补丁patch文件和老RN包生成一个新RN包。

安装

brew install bsdiff

使用bsdiff生成*.patched补丁文件

bsdiff /Users/xxx/Desktop/test/hot_old.zip /Users/xxx/Desktop/test/hot_new.zip /Users/xxx/Desktop/test/hot.patched

使用bspatch生成新包文件

bspatch /Users/javalong/Desktop/test/hot_old.zip /Users/javalong/Desktop/test/hot_new_patch.zip /Users/javalong/Desktop/test/hot.patched

验证生成的新包是否正确，两个md5相同，则生成是正确的

md5 /Users/xxx/Desktop/test/hot_new.zip

md5 /Users/xxx/Desktop/test/hot_new_patch.zip

iOS上的patch代码实现

#include "bspatch.h"
#include <sys/cdefs.h>

#include <bzlib.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <err.h>
#include <unistd.h>
#include <fcntl.h>

typedef unsigned char u_char;

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 beginPatch(const char* oldfile, const char* newfile, const char* patchfile)
{
    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(patchfile, "r")) == NULL) {
        //        err(1, "fopen(%s)", patchfile);
        return -1;
    }
    
    /*
     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");
        return -1;
    }
    
    /* 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))
        return -1;
    if ((cpf = fopen(patchfile, "r")) == NULL)
        return -1;
    if (fseeko(cpf, 32, SEEK_SET))
        return -1;
    if ((cpfbz2 = BZ2_bzReadOpen(&cbz2err, cpf, 0, 0, NULL, 0)) == NULL)
        return -1;
    if ((dpf = fopen(patchfile, "r")) == NULL)
        return -1;
    if (fseeko(dpf, 32 + bzctrllen, SEEK_SET))
        return -1;
    if ((dpfbz2 = BZ2_bzReadOpen(&dbz2err, dpf, 0, 0, NULL, 0)) == NULL)
        return -1;
    if ((epf = fopen(patchfile, "r")) == NULL)
        return -1;
    if (fseeko(epf, 32 + bzctrllen + bzdatalen, SEEK_SET))
        return -1;
    if ((epfbz2 = BZ2_bzReadOpen(&ebz2err, epf, 0, 0, NULL, 0)) == NULL)
        return -1;
    
    if(((fd=open(oldfile,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",oldfile);
    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)", patchfile);
        return -1;
    }
    
    /* Write the new file */
    if(((fd=open(newfile,O_CREAT|O_TRUNC|O_WRONLY,0666))<0) ||
       (write(fd,new,newsize)!=newsize) || (close(fd)==-1)) {
        err(1,"%s",newfile);
        return -1;
    }
    
    free(new);
    free(old);
    
    return 0;
}

Android上的patch代码实现

https://github.com/wangkunlin/Bsdiff-Bspatch/tree/master/Bsdiffwkl
https://github.com/jinyaqiao1102/Bsdiff-BspatchAndroid
JNI的使用
http://m.blog.csdn.net/article/details?id=51476144
这个让客户端开发实现好了。