[Zlib]_[初级]_[使用zlib库压缩和解压STL string]

场景

1.一般在使用文本json传输数据, 数据量特别大时,传输的过程就特别耗时, 因为带宽或者socket的缓存是有限制的, 数据量越大, 传输时间就越长. 网站一般使用gzip来压缩成二进制.

说明

1.zlib库可以实现gzip和zip方式的压缩, 这里只介绍zip方式的二进制压缩, 压缩比还是比较可观的, 一般写客户端程序已足够.

2.修改了一下zpipe.c的实现, 其实就是把读文件改为读字符串, 写文件改为写字符串即可.

例子

// test_zlib.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"

#include <string>
#include <iostream>
#include <memory>
#include <assert.h>
#include "zlib.h"

// E:\software\Lib\compress\zlib-1.2.5\src\examples
// zpipe.c

#define CHUNK 16384

/* Compress from file source to file dest until EOF on source.
   def() returns Z_OK on success, Z_MEM_ERROR if memory could not be
   allocated for processing, Z_STREAM_ERROR if an invalid compression
   level is supplied, Z_VERSION_ERROR if the version of zlib.h and the
   version of the library linked do not match, or Z_ERRNO if there is
   an error reading or writing the files. */
int CompressString(const char* in_str,size_t in_len,
    std::string& out_str, int level)
{
    if(!in_str)
        return Z_DATA_ERROR;

    int ret, flush;
    unsigned have;
    z_stream strm;

    unsigned char out[CHUNK];

    /* allocate deflate state */
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    strm.opaque = Z_NULL;
    ret = deflateInit(&strm, level);
    if (ret != Z_OK)
        return ret;

    std::shared_ptr<z_stream> sp_strm(&strm,[](z_stream* strm){
         (void)deflateEnd(strm);
    });
    const char* end = in_str+in_len;

    size_t pos_index = 0;
    size_t distance = 0;
    /* compress until end of file */
    do {
        distance = end - in_str;
        strm.avail_in = (distance>=CHUNK)?CHUNK:distance;
        strm.next_in = (Bytef*)in_str;

        // next pos
        in_str+= strm.avail_in;
        flush = (in_str == end) ? Z_FINISH : Z_NO_FLUSH;

        /* run deflate() on input until output buffer not full, finish
           compression if all of source has been read in */
        do {
            strm.avail_out = CHUNK;
            strm.next_out = out;
            ret = deflate(&strm, flush);    /* no bad return value */
            if(ret == Z_STREAM_ERROR)
                break;
            have = CHUNK - strm.avail_out;
            out_str.append((const char*)out,have);
        } while (strm.avail_out == 0);
        if(strm.avail_in != 0);     /* all input will be used */
            break;

        /* done when last data in file processed */
    } while (flush != Z_FINISH);
    if(ret != Z_STREAM_END)  /* stream will be complete */
        return Z_STREAM_ERROR;

    /* clean up and return */
    return Z_OK;
}

/* Decompress from file source to file dest until stream ends or EOF.
   inf() returns Z_OK on success, Z_MEM_ERROR if memory could not be
   allocated for processing, Z_DATA_ERROR if the deflate data is
   invalid or incomplete, Z_VERSION_ERROR if the version of zlib.h and
   the version of the library linked do not match, or Z_ERRNO if there
   is an error reading or writing the files. */
int DecompressString(const char* in_str,size_t in_len, std::string& out_str)
{
    if(!in_str)
        return Z_DATA_ERROR;

    int ret;
    unsigned have;
    z_stream strm;
    unsigned char out[CHUNK];

    /* allocate inflate state */
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    strm.opaque = Z_NULL;
    strm.avail_in = 0;
    strm.next_in = Z_NULL;
    ret = inflateInit(&strm);
    if (ret != Z_OK)
        return ret;

    std::shared_ptr<z_stream> sp_strm(&strm,[](z_stream* strm){
         (void)inflateEnd(strm);
    });

    const char* end = in_str+in_len;

    size_t pos_index = 0;
    size_t distance = 0;

    int flush = 0;
    /* decompress until deflate stream ends or end of file */
    do {
        distance = end - in_str;
        strm.avail_in = (distance>=CHUNK)?CHUNK:distance;
        strm.next_in = (Bytef*)in_str;

        // next pos
        in_str+= strm.avail_in;
        flush = (in_str == end) ? Z_FINISH : Z_NO_FLUSH;

        /* run inflate() on input until output buffer not full */
        do {
            strm.avail_out = CHUNK;
            strm.next_out = out;
            ret = inflate(&strm, Z_NO_FLUSH);
            if(ret == Z_STREAM_ERROR)  /* state not clobbered */
                break;
            switch (ret) {
            case Z_NEED_DICT:
                ret = Z_DATA_ERROR;     /* and fall through */
            case Z_DATA_ERROR:
            case Z_MEM_ERROR:
                return ret;
            }
            have = CHUNK - strm.avail_out;
            out_str.append((const char*)out,have);
        } while (strm.avail_out == 0);

        /* done when inflate() says it's done */
    } while (flush != Z_FINISH);

    /* clean up and return */
    return ret == Z_STREAM_END ? Z_OK : Z_DATA_ERROR;
}

int _tmain(int argc, _TCHAR* argv[])
{
    const char* buf  = "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "01010101010101010101010000000000000000000000000000011111111111111"
        "qwertyuiop[]";

    std::cout << "========= CompressString ===========" << std::endl;
    std::cout << "Source Buffer Size: " << strlen(buf) << std::endl;
    std::string out_compress;
    assert(CompressString(buf,strlen(buf),out_compress,Z_DEFAULT_COMPRESSION) == Z_OK);
    std::cout << "Compress Buffer Size: " << out_compress.size() << std::endl;

    std::cout << "========= DecompressString ===========" << std::endl;
    std::string out_decompress;
    assert(DecompressString(out_compress.c_str(),out_compress.size(),out_decompress) == Z_OK);
    std::cout << "Decompress Buffer Size: " << out_decompress.size() << std::endl;
    assert(!out_decompress.compare(buf));

    return 0;
}

输出:

========= CompressString ===========
Source Buffer Size: 662
Compress Buffer Size: 38
========= DecompressString ===========
Decompress Buffer Size: 662

参考

zlib\src\examples\zpipe.c

C++ Code Snippet - Compressing STL Strings with zlib