C语言压缩文件和用MD5算法校验文件完整性的实例教程

使用lzma SDK对7z文件简单解压缩
有时候我们只需要单纯对lzma算法压缩的7z文件进行解压，有时需要在嵌入式设备上解压，使用p7zip虽然支持多种格式，但是不容易裁剪，使用lzma SDK是首选：
可以在这里找到各种版本：http://zh.sourceforge.jp/projects/sfnet_sevenzip/releases/
我下载了4.65版本，这个对文件名编码支持没有9.20的好，中文可能有问题，但是我的需求不需要支持中文文件名，所以足够用了。
解压后先看一下7z这个工程，这个示例只有文件解压操作，仿照就可以写一个更加精简的解压函数：
需要的文件可以参考实例：

修改7zMain.c即可。
我们的目的是写一个函数extract7z，接收参数是7z文件路径，输出文件路径，便可执行全部解压。
主要调用函数：

SRes SzArEx_Open(CSzArEx *p, ILookInStream *inStream, ISzAlloc *allocMain, ISzAlloc *allocTemp); 

SRes SzAr_Extract(
  const CSzArEx *p,
  ILookInStream *inStream,
  UInt32 fileIndex,
  UInt32 *blockIndex,
  Byte **outBuffer,
  size_t *outBufferSize,
  size_t *offset,
  size_t *outSizeProcessed,
  ISzAlloc *allocMain,
  ISzAlloc *allocTemp);

我们先在Windows下编译：
完整代码如下：

/* 7zMain.c - Test application for 7z Decoder
*/ 

#include <stdlib.h>
#include <stdio.h>
#include <string.h> 

#define LOGD printf
#define LOGE printf 

#include "7zCrc.h"
#include "7zFile.h"
#include "7zVersion.h" 

#include "7zAlloc.h"
#include "7zExtract.h"
#include "7zIn.h" 

int MY_CDECL extract7z(const char* srcFile, const char* dstPath)
{
  CFileInStream archiveStream;
  CLookToRead lookStream;
  CSzArEx db;
  SRes res;
  ISzAlloc allocImp;
  ISzAlloc allocTempImp;
  char outPath[1024] = { 0 }; 

  LOGD("7z ANSI-C Decoder " MY_VERSION_COPYRIGHT_DATE "\n"); 

  if (InFile_Open(&archiveStream.file, srcFile)) {//open 7z file
    LOGE("can not open input file\n");
    return 1;
  } 

  FileInStream_CreateVTable(&archiveStream);
  LookToRead_CreateVTable(&lookStream, False); 

  lookStream.realStream = &archiveStream.s;
  LookToRead_Init(&lookStream); 

  allocImp.Alloc = SzAlloc;
  allocImp.Free = SzFree; 

  allocTempImp.Alloc = SzAllocTemp;
  allocTempImp.Free = SzFreeTemp; 

  CrcGenerateTable(); 

  SzArEx_Init(&db);
  res = SzArEx_Open(&db, &lookStream.s, &allocImp, &allocTempImp); 

  if(res == SZ_OK)
  {
    Int32 i; 

    UInt32 blockIndex = 0xFFFFFFFF; /* it can have any value before first call (if outBuffer = 0) */
    Byte *outBuffer = 0; /* it must be 0 before first call for each new archive. */
    size_t outBufferSize = 0; /* it can have any value before first call (if outBuffer = 0) */ 

    LOGD("Total file/directory count[%d]\n", db.db.NumFiles);
    for (i = db.db.NumFiles - 1; i >= 0; i--) {
      size_t offset;
      size_t outSizeProcessed;
      CSzFileItem *f = db.db.Files + i; 

      strcpy(outPath, dstPath);
      strcat(outPath, "/");
      strcat(outPath, f->Name); 

      if (f->IsDir) { //dir
        LOGD("dir [%s]\n", outPath);
        mkdir(outPath);
        continue;
      }else{ //file
        LOGD("file [%s]\n", outPath);
        res = SzAr_Extract(&db, &lookStream.s, i, &blockIndex,
            &outBuffer, &outBufferSize, &offset, &outSizeProcessed,
            &allocImp, &allocTempImp);
        if (res != SZ_OK){
          break;
        }else{
          CSzFile outFile;
          size_t processedSize;
          if (OutFile_Open(&outFile, outPath)) {
            LOGE("can not open output file\n");
            res = SZ_ERROR_FAIL;
            break;
          }
          processedSize = outSizeProcessed;
          if (File_Write(&outFile, outBuffer + offset, &processedSize)
              != 0 || processedSize != outSizeProcessed) {
            LOGE("can not write output file\n");
            res = SZ_ERROR_FAIL;
            break;
          }
          if (File_Close(&outFile)) {
            LOGE("can not close output file\n");
            res = SZ_ERROR_FAIL;
            break;
          }
        }
      }
    }
    IAlloc_Free(&allocImp, outBuffer);
  }
  SzArEx_Free(&db, &allocImp); 

  File_Close(&archiveStream.file);
  if (res == SZ_OK)
  {
    LOGD("Everything is Ok\n");
    return 0;
  }
  if (res == SZ_ERROR_UNSUPPORTED
    )
    LOGE("decoder doesn't support this archive\n");
  else if (res == SZ_ERROR_MEM
    )
    LOGE("can not allocate memory\n");
  else if (res == SZ_ERROR_CRC
    )
    LOGE("CRC error\n");
  else
    LOGE("ERROR #%d\n", res);
  return 1;
} 

int main(int numargs, char *args[])
{
  return extract7z(args[1], args[2]);
}

我用的是Eclipse，使用Mingw编译。

执行效果，能正确解压。
这样的解压只能适用简单的解压，不支持加密，参数2的输出文件路径中的所有文件夹都必须存在，压缩包中文件夹不需要存在，解压时会自动创建。
压缩包中的文件夹不能为中文，否则乱码。

使用MD5算法验证文件完整性或密码正确性
MD5即Message-Digest Algorithm 5（信息-摘要算法5），用于确保信息传输完整一致。是计算机广泛使用的杂凑算法之一（又译摘要算法、哈希算法），主流编程语言普遍已有MD5实现。
将数据（如汉字）运算为另一固定长度值，是杂凑算法的基础原理，MD5的前身有MD2、MD3和MD4。
MD5的作用是让大容量信息在用数字签名软件签署私人密钥前被"压缩"成一种保密的格式（就是把一个任意长度的字节串变换成一定长的十六进制数字串）。
MD5在实际应用中通常有两种用法，一种是计算一个字符串的MD5值，常用于密码相关的操作；另一种是用于计算一个文件的MD5值，一般用于网络传输中验证文件是否出错。
下面是C语言的MD5计算程序，来自Stardict，网上流行的代码都大同小异：
 
md5.h

#ifndef MD5_H
#define MD5_H 

#ifdef __cplusplus
extern "C"
{
#endif             /* __cplusplus */ 

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif 

#ifdef HAVE_STDINT_H
  #include <stdint.h>
  typedef uint32_t uint32;
#else
  /* A.Leo.: this wont work on 16 bits platforms ;) */
  typedef unsigned uint32;
#endif 

#define MD5_FILE_BUFFER_LEN 1024 

struct MD5Context {
  uint32 buf[4];
  uint32 bits[2];
  unsigned char in[64];
}; 

void MD5Init(struct MD5Context *context);
void MD5Update(struct MD5Context *context, unsigned char const *buf,
      unsigned len);
void MD5Final(unsigned char digest[16], struct MD5Context *context);
void MD5Transform(uint32 buf[4], uint32 const in[16]); 

int getBytesMD5(const unsigned char* src, unsigned int length, char* md5);
int getStringMD5(const char* src, char* md5);
int getFileMD5(const char* path, char* md5); 

/*
 * This is needed to make RSAREF happy on some MS-DOS compilers.
 */
typedef struct MD5Context MD5_CTX; 

#ifdef __cplusplus
}
#endif             /* __cplusplus */ 

#endif /* !MD5_H */

源文件：
md5.c

#include <string.h>    /* for memcpy() */
#include <stdio.h>
#include "md5.h" 

#ifndef HIGHFIRST
#define byteReverse(buf, len)  /* Nothing */
#else
void byteReverse(unsigned char *buf, unsigned longs); 

#ifndef ASM_MD5
/*
 * Note: this code is harmless on little-endian machines.
 */
void byteReverse(unsigned char *buf, unsigned longs)
{
  uint32 t;
  do {
    t = (uint32) ((unsigned) buf[3] << 8 | buf[2]) << 16 |
    ((unsigned) buf[1] << 8 | buf[0]);
    *(uint32 *) buf = t;
    buf += 4;
  }while (--longs);
}
#endif
#endif 

static void putu32(uint32 data, unsigned char *addr) {
  addr[0] = (unsigned char) data;
  addr[1] = (unsigned char) (data >> 8);
  addr[2] = (unsigned char) (data >> 16);
  addr[3] = (unsigned char) (data >> 24);
} 

/*
 * Start MD5 accumulation. Set bit count to 0 and buffer to mysterious
 * initialization constants.
 */
void MD5Init(struct MD5Context *ctx) {
  ctx->buf[0] = 0x67452301;
  ctx->buf[1] = 0xefcdab89;
  ctx->buf[2] = 0x98badcfe;
  ctx->buf[3] = 0x10325476; 

  ctx->bits[0] = 0;
  ctx->bits[1] = 0;
} 

/*
 * Update context to reflect the concatenation of another buffer full
 * of bytes.
 */
void MD5Update(struct MD5Context *ctx, unsigned char const *buf, unsigned len) {
  uint32 t; 

  /* Update bitcount */ 

  t = ctx->bits[0];
  if ((ctx->bits[0] = t + ((uint32) len << 3)) < t)
    ctx->bits[1]++; /* Carry from low to high */
  ctx->bits[1] += len >> 29; 

  t = (t >> 3) & 0x3f; /* Bytes already in shsInfo->data */ 

  /* Handle any leading odd-sized chunks */ 

  if (t) {
    unsigned char *p = (unsigned char *) ctx->in + t; 

    t = 64 - t;
    if (len < t) {
      memcpy(p, buf, len);
      return;
    }
    memcpy(p, buf, t);
    byteReverse(ctx->in, 16);
    MD5Transform(ctx->buf, (uint32 *) ctx->in);
    buf += t;
    len -= t;
  }
  /* Process data in 64-byte chunks */ 

  while (len >= 64) {
    memcpy(ctx->in, buf, 64);
    byteReverse(ctx->in, 16);
    MD5Transform(ctx->buf, (uint32 *) ctx->in);
    buf += 64;
    len -= 64;
  } 

  /* Handle any remaining bytes of data. */ 

  memcpy(ctx->in, buf, len);
} 

/*
 * Final wrapup - pad to 64-byte boundary with the bit pattern
 * 1 0* (64-bit count of bits processed, MSB-first)
 */
void MD5Final(unsigned char digest[16], struct MD5Context *ctx) {
  unsigned count;
  unsigned char *p; 

  /* Compute number of bytes mod 64 */
  count = (ctx->bits[0] >> 3) & 0x3F; 

  /* Set the first char of padding to 0x80. This is safe since there is
   always at least one byte free */
  p = ctx->in + count;
  *p++ = 0x80; 

  /* Bytes of padding needed to make 64 bytes */
  count = 64 - 1 - count; 

  /* Pad out to 56 mod 64 */
  if (count < 8) {
    /* Two lots of padding: Pad the first block to 64 bytes */
    memset(p, 0, count);
    byteReverse(ctx->in, 16);
    MD5Transform(ctx->buf, (uint32 *) ctx->in); 

    /* Now fill the next block with 56 bytes */
    memset(ctx->in, 0, 56);
  } else {
    /* Pad block to 56 bytes */
    memset(p, 0, count - 8);
  } byteReverse(ctx->in, 14); 

  /* Append length in bits and transform */
  //((uint32 *) ctx->in)[14] = ctx->bits[0];
  //((uint32 *) ctx->in)[15] = ctx->bits[1];
  putu32(ctx->bits[0], ctx->in + 56);
  putu32(ctx->bits[1], ctx->in + 60); 

  MD5Transform(ctx->buf, (uint32 *) ctx->in);
  byteReverse((unsigned char *) ctx->buf, 4);
  memcpy(digest, ctx->buf, 16);
  memset(ctx, 0, sizeof(*ctx)); /* In case it's sensitive */
} 

#ifndef ASM_MD5 

/* The four core functions - F1 is optimized somewhat */ 

/* #define F1(x, y, z) (x & y | ~x & z) */
#define F1(x, y, z) (z ^ (x & (y ^ z)))
#define F2(x, y, z) F1(z, x, y)
#define F3(x, y, z) (x ^ y ^ z)
#define F4(x, y, z) (y ^ (x | ~z)) 

/* This is the central step in the MD5 algorithm. */
#define MD5STEP(f, w, x, y, z, data, s) \
  ( w += f(x, y, z) + data, w = w<<s | w>>(32-s), w += x ) 

/*
 * The core of the MD5 algorithm, this alters an existing MD5 hash to
 * reflect the addition of 16 longwords of new data. MD5Update blocks
 * the data and converts bytes into longwords for this routine.
 */
void MD5Transform(uint32 buf[4], uint32 const in[16]) {
  register uint32 a, b, c, d; 

  a = buf[0];
  b = buf[1];
  c = buf[2];
  d = buf[3]; 

  MD5STEP(F1, a, b, c, d, in[0] + 0xd76aa478, 7);
  MD5STEP(F1, d, a, b, c, in[1] + 0xe8c7b756, 12);
  MD5STEP(F1, c, d, a, b, in[2] + 0x242070db, 17);
  MD5STEP(F1, b, c, d, a, in[3] + 0xc1bdceee, 22);
  MD5STEP(F1, a, b, c, d, in[4] + 0xf57c0faf, 7);
  MD5STEP(F1, d, a, b, c, in[5] + 0x4787c62a, 12);
  MD5STEP(F1, c, d, a, b, in[6] + 0xa8304613, 17);
  MD5STEP(F1, b, c, d, a, in[7] + 0xfd469501, 22);
  MD5STEP(F1, a, b, c, d, in[8] + 0x698098d8, 7);
  MD5STEP(F1, d, a, b, c, in[9] + 0x8b44f7af, 12);
  MD5STEP(F1, c, d, a, b, in[10] + 0xffff5bb1, 17);
  MD5STEP(F1, b, c, d, a, in[11] + 0x895cd7be, 22);
  MD5STEP(F1, a, b, c, d, in[12] + 0x6b901122, 7);
  MD5STEP(F1, d, a, b, c, in[13] + 0xfd987193, 12);
  MD5STEP(F1, c, d, a, b, in[14] + 0xa679438e, 17);
  MD5STEP(F1, b, c, d, a, in[15] + 0x49b40821, 22); 

  MD5STEP(F2, a, b, c, d, in[1] + 0xf61e2562, 5);
  MD5STEP(F2, d, a, b, c, in[6] + 0xc040b340, 9);
  MD5STEP(F2, c, d, a, b, in[11] + 0x265e5a51, 14);
  MD5STEP(F2, b, c, d, a, in[0] + 0xe9b6c7aa, 20);
  MD5STEP(F2, a, b, c, d, in[5] + 0xd62f105d, 5);
  MD5STEP(F2, d, a, b, c, in[10] + 0x02441453, 9);
  MD5STEP(F2, c, d, a, b, in[15] + 0xd8a1e681, 14);
  MD5STEP(F2, b, c, d, a, in[4] + 0xe7d3fbc8, 20);
  MD5STEP(F2, a, b, c, d, in[9] + 0x21e1cde6, 5);
  MD5STEP(F2, d, a, b, c, in[14] + 0xc33707d6, 9);
  MD5STEP(F2, c, d, a, b, in[3] + 0xf4d50d87, 14);
  MD5STEP(F2, b, c, d, a, in[8] + 0x455a14ed, 20);
  MD5STEP(F2, a, b, c, d, in[13] + 0xa9e3e905, 5);
  MD5STEP(F2, d, a, b, c, in[2] + 0xfcefa3f8, 9);
  MD5STEP(F2, c, d, a, b, in[7] + 0x676f02d9, 14);
  MD5STEP(F2, b, c, d, a, in[12] + 0x8d2a4c8a, 20); 

  MD5STEP(F3, a, b, c, d, in[5] + 0xfffa3942, 4);
  MD5STEP(F3, d, a, b, c, in[8] + 0x8771f681, 11);
  MD5STEP(F3, c, d, a, b, in[11] + 0x6d9d6122, 16);
  MD5STEP(F3, b, c, d, a, in[14] + 0xfde5380c, 23);
  MD5STEP(F3, a, b, c, d, in[1] + 0xa4beea44, 4);
  MD5STEP(F3, d, a, b, c, in[4] + 0x4bdecfa9, 11);
  MD5STEP(F3, c, d, a, b, in[7] + 0xf6bb4b60, 16);
  MD5STEP(F3, b, c, d, a, in[10] + 0xbebfbc70, 23);
  MD5STEP(F3, a, b, c, d, in[13] + 0x289b7ec6, 4);
  MD5STEP(F3, d, a, b, c, in[0] + 0xeaa127fa, 11);
  MD5STEP(F3, c, d, a, b, in[3] + 0xd4ef3085, 16);
  MD5STEP(F3, b, c, d, a, in[6] + 0x04881d05, 23);
  MD5STEP(F3, a, b, c, d, in[9] + 0xd9d4d039, 4);
  MD5STEP(F3, d, a, b, c, in[12] + 0xe6db99e5, 11);
  MD5STEP(F3, c, d, a, b, in[15] + 0x1fa27cf8, 16);
  MD5STEP(F3, b, c, d, a, in[2] + 0xc4ac5665, 23); 

  MD5STEP(F4, a, b, c, d, in[0] + 0xf4292244, 6);
  MD5STEP(F4, d, a, b, c, in[7] + 0x432aff97, 10);
  MD5STEP(F4, c, d, a, b, in[14] + 0xab9423a7, 15);
  MD5STEP(F4, b, c, d, a, in[5] + 0xfc93a039, 21);
  MD5STEP(F4, a, b, c, d, in[12] + 0x655b59c3, 6);
  MD5STEP(F4, d, a, b, c, in[3] + 0x8f0ccc92, 10);
  MD5STEP(F4, c, d, a, b, in[10] + 0xffeff47d, 15);
  MD5STEP(F4, b, c, d, a, in[1] + 0x85845dd1, 21);
  MD5STEP(F4, a, b, c, d, in[8] + 0x6fa87e4f, 6);
  MD5STEP(F4, d, a, b, c, in[15] + 0xfe2ce6e0, 10);
  MD5STEP(F4, c, d, a, b, in[6] + 0xa3014314, 15);
  MD5STEP(F4, b, c, d, a, in[13] + 0x4e0811a1, 21);
  MD5STEP(F4, a, b, c, d, in[4] + 0xf7537e82, 6);
  MD5STEP(F4, d, a, b, c, in[11] + 0xbd3af235, 10);
  MD5STEP(F4, c, d, a, b, in[2] + 0x2ad7d2bb, 15);
  MD5STEP(F4, b, c, d, a, in[9] + 0xeb86d391, 21); 

  buf[0] += a;
  buf[1] += b;
  buf[2] += c;
  buf[3] += d;
} 

/*
 * get MD5 of a byte buffer
 */
int getBytesMD5(const unsigned char* src, unsigned int length, char* md5) {
  unsigned char i = 0;
  unsigned char md5Bytes[16] = { 0 };
  MD5_CTX context;
  if (src == NULL || md5 == NULL)
  {
    return -1;
  }
  MD5Init(&context);
  MD5Update(&context, src, length);
  MD5Final(md5Bytes, &context);
  for (i = 0; i < 16; i++) {
    sprintf(md5, "%02X", md5Bytes[i]);
    md5 += 2;
  }
  *md5 = '\0';
  return 0;
} 

/*
 * get MD5 for a string
 */
int getStringMD5(const char* src, char* md5) {
  return getBytesMD5((unsigned char*) src, strlen((char*) src), md5);
} 

/**
 * get MD5 of a file
 */
int getFileMD5(const char* path, char* md5) {
  FILE* fp = NULL;
  unsigned char buffer[MD5_FILE_BUFFER_LEN] = { 0 };
  int count = 0;
  MD5_CTX context;
  unsigned char md5Bytes[16] = { 0 };
  int i;
  if (path == NULL || md5 == NULL) {
    return -1;
  }
  fp = fopen(path, "rb");
  if (fp == NULL) {
    return -1;
  }
  MD5Init(&context);
  while ((count = fread(buffer, 1, MD5_FILE_BUFFER_LEN, fp)) > 0) {
    MD5Update(&context, buffer, count);
  }
  MD5Final(md5Bytes, &context);
  for (i = 0; i < 16; i++) {
    sprintf(md5, "%02X", md5Bytes[i]);
    md5 += 2;
  }
  *md5 = '\0';
  return 0;
} 

#endif

下面是调用函数计算MD5的代码：
 main.c

#include <stdio.h>
#include <string.h> 

#include "md5.h" 

int main(int c, char** v){
  char buffer[128];
  getStringMD5("hello world", buffer);
  printf("%s\n", buffer);
  getFileMD5("hello.pdf", buffer);
  printf("%s\n", buffer);
  return 0;
} 

计算无误：