使用案例

ZSTD压缩算法提供了两种常见的接口调用方式：CTX接口和简单接口。本章节以简单接口调用KZstar库为例提供完整的接口使用示例。

CTX接口：提供了更高的灵活性和控制，允许用户通过管理压缩/解压上下文（ZSTD_CCtx和ZSTD_DCtx）来进行更细粒度的操作。使用CTX接口，用户可以手动控制压缩过程中的各项参数，并且能够更加精细地调整压缩行为。
简单接口：相较于CTX接口，简单接口则提供了更加简洁和易用的调用方式。用户无需关心上下文的管理和复杂的参数配置。

CTX接口示例

char* zstd_init()
{
    zstd_params_s* zstd_params = (zstd_params_s*) malloc(sizeof(zstd_params_s));
    if (!zstd_params) return NULL;
    zstd_params->cctx = ZSTD_createCCtx();
    zstd_params->dctx = ZSTD_createDCtx();
    zstd_params->cdict = NULL;
    return (char*) zstd_params;
}

int64_t zstd_compress(char *inbuf, size_t insize, char *outbuf, size_t outsize, size_t level, char* workmem)
{
    size_t res;

    zstd_params_s* zstd_params = (zstd_params_s*) workmem;
    if (!zstd_params || !zstd_params->cctx) return 0;

    zstd_params->zparams = ZSTD_getParams(level, insize, 0);
    ZSTD_CCtx_setParameter(zstd_params->cctx, ZSTD_c_compressionLevel, level);
    zstd_params->zparams.fParams.contentSizeFlag = 1;

    res = ZSTD_compressCCtx(zstd_params->cctx, outbuf, outsize, inbuf, insize, level);
    if (ZSTD_isError(res)) return res;

    return res;
}

int64_t zstd_decompress(char *inbuf, size_t insize, char *outbuf, size_t outsize, char* workmem)
{
    zstd_params_s* zstd_params = (zstd_params_s*) workmem;
    if (!zstd_params || !zstd_params->dctx) return 0;

    return ZSTD_decompressDCtx(zstd_params->dctx, outbuf, outsize, inbuf, insize);
}

void zstd_deinit(char* workmem)
{
    zstd_params_s* zstd_params = (zstd_params_s*) workmem;
    if (!zstd_params) return;
    if (zstd_params->cctx) ZSTD_freeCCtx(zstd_params->cctx);
    if (zstd_params->dctx) ZSTD_freeDCtx(zstd_params->dctx);
    if (zstd_params->cdict) ZSTD_freeCDict(zstd_params->cdict);
    free(workmem);
}

简单接口示例

// 1. 输入数据
const char *input_data = "This is the input data that we want to compress using ZSTAR!";
size_t insize = strlen(input_data) + 1;

// 2. 分配内存
size_t compress_bound = ZSTD_compressBound(insize);
void *outbuf = malloc(compress_bound);

// 3. 压缩数据
size_t compressed_size = ZSTD_compress(outbuf, compress_bound, input_data, insize, 3);  // 使用压缩级别 3

// 4. 解压数据
size_t dst_size = ZSTD_getFrameContentSize(outbuf, compressed_size); // 获取解压后的数据大小
void *decompressed_data = malloc(dst_size);
size_t decompressed_size = ZSTD_decompress(decompressed_data, dst_size, outbuf, compressed_size);

简单接口使能KZstar示例

以简单接口调用为例，编写验证程序。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <zstd.h> 

int main() {
    const char *input_data = "This is the input data that we want to compress using KZSTAR!";
    size_t insize = strlen(input_data) + 1; 

    size_t compress_bound = ZSTD_compressBound(insize); 
    void *outbuf = malloc(compress_bound);
    if (outbuf == NULL) {
        fprintf(stderr, "Failed to allocate memory for compression buffer.\n");
        return 1;
    }

    size_t compressed_size = ZSTD_compress(outbuf, compress_bound, input_data, insize, 3); 
    if (ZSTD_isError(compressed_size)) {
        fprintf(stderr, "Compression failed: %s\n", ZSTD_getErrorName(compressed_size));
        free(outbuf);
        return 1;
    }

    printf("Data successfully compressed! Compressed size: %zu\n", compressed_size);

    size_t dst_size = ZSTD_getFrameContentSize(outbuf, compressed_size);
    void *decompressed_data = malloc(dst_size); 
    if (decompressed_data == NULL) {
        fprintf(stderr, "Failed to allocate memory for decompression buffer.\n");
        free(outbuf);
        return 1;
    }

    size_t decompressed_size = ZSTD_decompress(decompressed_data, dst_size, outbuf, compressed_size);
    if (ZSTD_isError(decompressed_size)) {
        fprintf(stderr, "Decompression failed: %s\n", ZSTD_getErrorName(decompressed_size));
        free(outbuf);
        free(decompressed_data);
        return 1;
    }

    printf("Data successfully decompressed! Decompressed size: %zu\n", decompressed_size);
    printf("Decompressed data: %s\n", (char *)decompressed_data);

    free(outbuf);
    free(decompressed_data);

    return 0;
}

根据KZstar的安装位置，配置对应环境变量。

export LD_LIBRARY_PATH=/usr/local/kzstar/lib:$LD_LIBRARY_PATH

编译程序。

gcc -o ZstdSimpleCompress ZstdSimpleCompress.c -lzstd

查看是否正确链接KZstar库。

1	ldd ZstdSimpleCompress

回显如下所示，表示程序已正确链接KZstar库。

 linux-vdso.so.1 (0x0000ffff83646000)
 libzstd.so.1 => /usr/local/kzstar/lib/libzstd.so.1 (0x0000ffff83528000)
 libc.so.6 => /usr/lib64/libc.so.6 (0x0000ffff83379000)
 libzstar.so => /usr/local/kzstar/lib/libzstar.so (0x0000ffff83348000)
 /lib/ld-linux-aarch64.so.1 (0x0000ffff83609000)
 libsecurec.so => /usr/local/kzstar/lib/libsecurec.so (0x0000ffff83317000)

运行可执行程序。

./ZstdSimpleCompress 

输出结果如下。

Data successfully compressed! Compressed size: 70
Data successfully decompressed! Decompressed size: 61
Decompressed data: This is the input data that we want to compress using KZSTAR!