使用zlib压缩和解压gzip

基于zlib，写了两个函数，可以压缩和解压gzip格式的char *数据。

main里面进行了一下包装，实现了压缩和解压gzip文件的功能。

linux上的标准gzip程序会将原始文件名记录在gzip文件的起始处，后面的内容则同下面程序的操作结果完全相同。所以标准gzip的压缩结果总是比下面程序的压缩结果多几个字节，不过这几个字节不影响解压。

如果需要成功编译该程序，可能需要修改下面zlib头文件的位置到你的环境中的正确位置。

/*************************************************************************** * 
 * Copyright (c) 2015 Xxx.com, Inc. All Rights Reserved
 * 
 **************************************************************************/
 
 
 
/**
 * @file main.cpp
 * @author xxx([email protected])
 * @date 2015/01/07 11:46:57
 * @brief 
 *  
 **/

#include 
#include 
#include 
#include 
#include  // "zlib.h" ?

#define windowBits 15
#define ENABLE_ZLIB_GZIP 32
#define GZIP_ENCODING 16

/**
 * @brief
 * @param dest_len big enough to hold the result 
 */
int decompress (unsigned char *src, size_t src_len, unsigned char *dest, size_t dest_len)
{
    z_stream strm;

    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    strm.opaque = Z_NULL;
    strm.next_in = src;
    strm.avail_in = src_len;
    strm.next_out = dest;
    strm.avail_out = dest_len;
    if (inflateInit2 (& strm, windowBits | ENABLE_ZLIB_GZIP) < 0){ 
        printf("init failed\n");
        return -1; 
    }   
    if (inflate (& strm, Z_NO_FLUSH) < 0){ 
        printf("inflate failed %s\n", "");
        return -1; 
    }   
    inflateEnd (& strm);
    return dest_len - strm.avail_out;
}
/**
 * @brief
 * @param
 */
int compress (unsigned char *src, size_t src_len, unsigned char *dest, size_t dest_len)
{
    z_stream strm;
    strm.zalloc = Z_NULL;
    strm.zfree  = Z_NULL;
    strm.opaque = Z_NULL;
    if (deflateInit2 (&strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED,
                             windowBits | GZIP_ENCODING, 8,
                             Z_DEFAULT_STRATEGY) < 0){ 
        printf("init failed\n");
        return -1; 
    }   

    strm.next_in = src;
    strm.avail_in = src_len;

    strm.avail_out = dest_len;
    strm.next_out = dest;
    if (deflate (& strm, Z_FINISH) < 0){ 
        printf("deflate failed\n");
        return -1; 
    }    
    deflateEnd (& strm);
    return dest_len - strm.avail_out;
}


int main(int argc, char *argv[])
{
    if (argc != 4) {
        printf("format error\n\tformat: %s [d|c] inputfile outputfile\n\tuse 'd' for decompress, 'c' for compress\n", argv[0]);
        return -1;
    }       

    // get input & output file name
    const char * input_file_name = argv[2];
    const char * output_file_name = argv[3];

    // open input file, and get the size of the file
    FILE * fp = fopen (input_file_name, "rb");
    if (!fp){
        printf("open file failed\n");
        return -1;
    }       
    fseek(fp, 0, SEEK_END);
    int file_len = ftell(fp);
    printf("file len %d\n", file_len);
    fseek(fp, 0, SEEK_SET);

    // allocate enough memory to hold the input file
    unsigned char *src;
    src = (unsigned char*)malloc(file_len);

    // load the input file
    int bytes_read = fread (src, 1, file_len, fp);
    fclose(fp);
    if (bytes_read != file_len){
        printf("read file error[%d != %d]\n", bytes_read, file_len);
        free(src);
        return -1;
    }       
        
    // allocate enough memory to hold the result
    int dest_len;
    if (argv[1][0] == 'd'){
        dest_len = file_len * 10; 
    }else{
        dest_len = file_len;
    }
    unsigned char *dest;
    dest = (unsigned char*)malloc(dest_len);

    // do the work
    int size;
    if (argv[1][0] == 'd'){
        size = decompress(src, file_len, dest, dest_len);
    }else{
        size = compress(src, file_len, dest, dest_len);
    }

    // save the result to the given output file
    printf("out len %d\n", size);
    if (size > 0){
        fp = fopen(output_file_name, "wb");
        fwrite(dest, 1, size, fp); 
        fclose(fp);
    }else{
        printf("operation failed[code = %d]\n", size);
    }

    // free resources
    free(src);
    free(dest);
    return 0;

}


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