zlib压缩一个文件为gzip格式

网上有很多针对zlib的总结，但是很零散，自己经过总结，实现了用zlib压缩一个文件为gzip格式，似的可以直接使用winr工具解压。

具体方法是使用zlib的deflate系列函数，将buffer压缩为gzip格式，deflateInit2的参数注意使用MAX_WBITS+16，这样压缩后可以带gzip的头、尾信息。

然后将压缩后的内容直接写入到目标文件，保存为.gz， 使用WinR就可以直接解压了。

demo程序如下(deflate_gzip.c)：

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

 /*******************************************************************************
 * Compress gzip data
 * @parm[data] data buffer to be compressed
 * @parm[dlen] data buffer length
 * @parm[zdata] data buffer to save the compressed datas
 * @parm[zdlen] compressed data buffer length
 * return: 0 - OK; -1 - FAIL
 *******************************************************************************/
 int gzcompress(Bytef *data, uLong dlen, Bytef *zdata, uLong *zdlen)
 {
     int err = ;
     z_stream c_stream;

     printf("%s: data=%p, dlen=%lu, zdata=%p, *zdlen=%lu\n",
         __func__, data, dlen, zdata, *zdlen);

     if(data && dlen > )
     {
         c_stream.zalloc = NULL;
         c_stream.zfree = NULL;
         c_stream.opaque = NULL;
         //use parm 'MAX_WBITS+16' so that gzip headers are contained
         if(deflateInit2(&c_stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED,
             MAX_WBITS + , , Z_DEFAULT_STRATEGY) != Z_OK)
         {
             printf("%s: deflateinit2 failed!\n",__func__);
             return -;
         }
         c_stream.next_in  = data;
         c_stream.avail_in  = dlen;
         c_stream.next_out = zdata;
         c_stream.avail_out  = *zdlen;
         while(c_stream.avail_in !=  && c_stream.total_out < *zdlen)
         {
             if(deflate(&c_stream, Z_NO_FLUSH) != Z_OK) {
                 printf("%s: deflate failed!\n",__func__);
                 return -;
             }
         }
         if(c_stream.avail_in != ) {
             printf("%s: avail_in not zero!\n",__func__);
             return c_stream.avail_in;
         }
         for(;;)
         {
             if((err = deflate(&c_stream, Z_FINISH)) == Z_STREAM_END)
                 break;
             if(err != Z_OK) {
                 printf("%s: deflate finish fail: %d\n",__func__, err);
                 return -;
             }
         }
         if(deflateEnd(&c_stream) != Z_OK) {
             printf("%s: deflate end failed!\n",__func__);
             return -;
         }
         *zdlen = c_stream.total_out;
         return ;
     }
     return -;
 }

 /*******************************************************************************
 * Compress a file into a gzip file
 * @parm[input_name] the file path to be compressed
 * @parm[output_name] output path of compressed gzip file
 * return: 0 - OK; -1 - FAIL
 *******************************************************************************/
 int compress_file_to_gzip(char * input_name, char * output_name)
 {
     FILE *fp = NULL;
     uLong flen, clen;
     unsigned char * fbuf = NULL;
     unsigned char * cbuf = NULL;
     char def_output_name[PATH_MAX] = {};    

     if((fp = fopen(input_name, "rb")) == NULL)
     {
         printf("%s: can not open %s!\n", __func__, input_name);
         return -;
     }

     /*load file content to buffer*/
     fseek(fp, 0L, SEEK_END);
     flen = ftell(fp);
     fseek(fp, 0L, SEEK_SET);
     fbuf = (unsigned char *)malloc(flen * sizeof(unsigned char));
     if(NULL == fbuf){
         printf("%s: no enough memory!\n", __func__);
         goto __error;
     }
     fread(fbuf, sizeof(unsigned char), flen, fp);
     fclose(fp);
     fp = NULL;

     /*compute compressBound*/
     clen = compressBound(flen);
     cbuf = (unsigned char *)malloc(clen * sizeof(unsigned char));
     if(NULL == cbuf) {
         printf("%s: no enough memory!\n", __func__);
         goto __error;
     }

     if(gzcompress(fbuf, flen, cbuf, &clen))
     {
         printf("%s: compress %s failed!\n", __func__, input_name);
         goto __error;
     }

     if(NULL == output_name) {
         snprintf(def_output_name, sizeof(def_output_name),
         "%s.gz", input_name);
         output_name = def_output_name;
     }
     if((fp = fopen(output_name, "wb")) == NULL)
     {
         printf("%s: can not open %s!\n", __func__, output_name);
         goto __error;
     }
     fwrite(cbuf, sizeof(unsigned char), clen, fp);

     fclose(fp);
     free(fbuf);
     free(cbuf);
     return ;

 __error:
     if(fp) fclose(fp);
     if(fbuf) free(fbuf);
     if(cbuf) free(cbuf);
     return -;
 }

 int main(int argc, char * argv[])
 {
     if(argc < ) {
         printf("too few args!\n");
         return ;
     }

     if(argc < ) {
         return compress_file_to_gzip(argv[],NULL);
     }

     return compress_file_to_gzip(argv[], argv[]);
 }

编译命令：

gcc -o zlibtest deflate_gzip.c.c -lz

如果编译连接的时候示找不到deflate等函数，则需要安装zlib库，ubuntu下：

sudo apt-get install zlib1g zlib1g-dev zlibc

参考内容链接：

http://www.oschina.net/code/snippet_65636_22542

http://blog.csdn.net/turingo/article/details/8178510