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  
#include  
#include  
 
#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  
  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     /* for memcpy() */ 
#include  
#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<>(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  
#include  
 
#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：