使用zlib实现gzip格式数据的压缩和解压

注意代码中的注释部分，这里设置是专门针对gzip的，缺少了就不行了，gzip压缩格式和其他格式的区别就在这里。
Bytef 就是 unsigned char，uLong就是 unsigned long，这些别名的设置都在zconf.h文件里面。

这里压缩和解压缩的数据都可以用java的GZIPInputStream和GZIPOutputStream来对应解压缩和压缩。

代码片
#ifndef GZIP_H
#define GZIP_H

#include "zlib/zlib.h"

/* Compress gzip data */
/* data 原数据 ndata 原数据长度 zdata 压缩后数据 nzdata 压缩后长度 */
int gzcompress(Bytef *data, uLong ndata,
               Bytef *zdata, uLong *nzdata)
{
    z_stream c_stream;
int err = 0;

if(data && ndata > 0) {
        c_stream.zalloc = NULL;
        c_stream.zfree = NULL;
        c_stream.opaque = NULL;
//只有设置为MAX_WBITS + 16才能在在压缩文本中带header和trailer
if(deflateInit2(&c_stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED,
                        MAX_WBITS + 16, 8, Z_DEFAULT_STRATEGY) != Z_OK) return -1;
        c_stream.next_in  = data;
        c_stream.avail_in  = ndata;
        c_stream.next_out = zdata;
        c_stream.avail_out  = *nzdata;
while(c_stream.avail_in != 0 && c_stream.total_out < *nzdata) {
if(deflate(&c_stream, Z_NO_FLUSH) != Z_OK) return -1;
        }
if(c_stream.avail_in != 0) return c_stream.avail_in;
for(;;) {
if((err = deflate(&c_stream, Z_FINISH)) == Z_STREAM_END) break;
if(err != Z_OK) return -1;
        }
if(deflateEnd(&c_stream) != Z_OK) return -1;
        *nzdata = c_stream.total_out;
return 0;
    }
return -1;
}

/* Uncompress gzip data */
/* zdata 数据 nzdata 原数据长度 data 解压后数据 ndata 解压后长度 */
int gzdecompress(Byte *zdata, uLong nzdata,
                 Byte *data, uLong *ndata)
{
int err = 0;
    z_stream d_stream = {0}; /* decompression stream */
static char dummy_head[2] = {
0x8 + 0x7 * 0x10,
        (((0x8 + 0x7 * 0x10) * 0x100 + 30) / 31 * 31) & 0xFF,
    };
    d_stream.zalloc = NULL;
    d_stream.zfree = NULL;
    d_stream.opaque = NULL;
    d_stream.next_in  = zdata;
    d_stream.avail_in = 0;
    d_stream.next_out = data;
//只有设置为MAX_WBITS + 16才能在解压带header和trailer的文本
if(inflateInit2(&d_stream, MAX_WBITS + 16) != Z_OK) return -1;
//if(inflateInit2(&d_stream, 47) != Z_OK) return -1;
while(d_stream.total_out < *ndata && d_stream.total_in < nzdata) {
        d_stream.avail_in = d_stream.avail_out = 1; /* force small buffers */
if((err = inflate(&d_stream, Z_NO_FLUSH)) == Z_STREAM_END) break;
if(err != Z_OK) {
if(err == Z_DATA_ERROR) {
                d_stream.next_in = (Bytef*) dummy_head;
                d_stream.avail_in = sizeof(dummy_head);
if((err = inflate(&d_stream, Z_NO_FLUSH)) != Z_OK) {
return -1;
                }
            } else return -1;
        }
    }
if(inflateEnd(&d_stream) != Z_OK) return -1;
    *ndata = d_stream.total_out;
return 0;
}

#endif // GZIP_H