C语言使用 gzip 算法压缩数据

前言

在实际工作场景中，为了节省网络带宽，经常需要将大的数据压缩后传输。gzip 是一种很常见的数据压缩算法，本文给出C语言程序实例，介绍如何使用 zlib 库中的 gzip 算法压缩数据。

代码

test_zlib.c 代码如下：

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

#include "zlib.h"

int data_compress(char *idata, int ilen, char *odata, int *olen)
{
    z_stream z = {0};

    z.next_in = idata;
    z.avail_in = ilen;
    z.next_out = odata;
    z.avail_out = *olen;
 
    printf("total %u bytes\n", z.avail_in);
 
    /* 使用最高压缩比 */
    if (deflateInit(&z, Z_BEST_COMPRESSION) != Z_OK) {
        printf("deflateInit failed!\n");
        return -1;
    }

    if (deflate(&z, Z_NO_FLUSH) != Z_OK) {
        printf("deflate Z_NO_FLUSH failed!\n");
        return -1;
    }

    if (deflate(&z, Z_FINISH) != Z_STREAM_END) {
        printf("deflate Z_FINISH failed!\n");
        return -1;
    }

    if (deflateEnd(&z) != Z_OK) {
        printf("deflateEnd failed!\n");
        return -1;
    }
 
    *olen = *olen - z.avail_out;

    printf("compressed data %d bytes.\n", *olen);

    return 0;
}


int data_decompress(char *idata, int ilen, char *odata, int *olen)
{
    z_stream z = {0};

    z.next_in = idata;
    z.avail_in = ilen;
    z.next_out = odata;
    z.avail_out = *olen;

    if (inflateInit(&z) != Z_OK) {
        printf("inflateInit failed!\n");
        return -1;
    }

    if (inflate(&z, Z_NO_FLUSH) != Z_STREAM_END) {
        printf("inflate Z_NO_FLUSH failed!\n");
        return -1;
    }

    if (inflate(&z, Z_FINISH) != Z_STREAM_END) {
        printf("inflate Z_FINISH failed!\n");
        return -1;
    }

    if (inflateEnd(&z) != Z_OK) {
        printf("inflateEnd failed!\n");
        return -1;
    }

    *olen = strlen(odata);
    
    printf("decompressed data: %s\n", odata);

}

char data[]="\nYouth\n\nYouth is not a time of life; it is a state of mind; it is not a matter of rosy cheeks, red lips and supple knees; it is a matter of the will, a quality of the imagination, a vigor of the emotions; it is the freshness of the deep springs of life.\n\nYouth means a temperamental predominance of courage over timidity, of the appetite for adventure over the love of ease. This often exists in a man of 60 more than a boy of 20. Nobody grows old merely by a number of years. We grow old by deserting our ideals.\n\nYears may wrinkle the skin, but to give up enthusiasm wrinkles the soul. Worry, fear, self-distrust bows the heart and turns the spirit back to dust.\n\nWhether 60 or 16, there is in every human being’s heart the lure of wonders, the unfailing appetite for what’s next and the joy of the game of living. In the center of your heart and my heart, there is a wireless station; so long as it receives messages of beauty, hope, courage and power from man and from the infinite, so long as you are young.\n\nWhen your aerials are down, and your spirit is covered with snows of cynicism and the ice of pessimism, then you’ve grown old, even at 20; but as long as your aerials are up, to catch waves of optimism, there’s hope you may die young at 80.";
 
int main(int argc, char **argv)
{
    int compress_len, decompress_len;
    char compress_buf[2048];
    char decompress_buf[4096];
    
    /* 压缩数据 */
    compress_len = sizeof(compress_buf);
    if (data_compress(data, strlen(data), 
                      compress_buf, &compress_len) < 0) {
        return -1;
    }

    /* 解压缩数据 */
    decompress_len = sizeof(decompress_buf);
    if (data_decompress(compress_buf, compress_len, 
                        decompress_buf, &decompress_len) < 0) {
        return -1;
    }
        
    return 0;
}

运行

执行 gcc -o test_zlib test_zlib.c -lz 编译，程序运行结果如下：

total 1262 bytes
compressed data 655 bytes.
decompressed data:
Youth

Youth is not a time of life; it is a state of mind; it is not a matter of rosy cheeks, red lips and supple knees; it is a matter of the will, a quality of the imagination, a vigor of the emotions; it is the freshness of the deep springs of life.

Youth means a temperamental predominance of courage over timidity, of the appetite for adventure over the love of ease. This often exists in a man of 60 more than a boy of 20. Nobody grows old merely by a number of years. We grow old by deserting our ideals.

Years may wrinkle the skin, but to give up enthusiasm wrinkles the soul. Worry, fear, self-distrust bows the heart and turns the spirit back to dust.

Whether 60 or 16, there is in every human being’s heart the lure of wonders, the unfailing appetite for what’s next and the joy of the game of living. In the center of your heart and my heart, there is a wireless station; so long as it receives messages of beauty, hope, courage and power from man and from the infinite, so long as you are young.

When your aerials are down, and your spirit is covered with snows of cynicism and the ice of pessimism, then you’ve grown old, even at 20; but as long as your aerials are up, to catch waves of optimism, there’s hope you may die young at 80.

可以看到原先数据长度是 1262 字节，压缩后是 655 字节，数据被压缩了近一半。