[Zlib]_[初级]_[使用zlib库压缩和解压字符串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: 662Compress Buffer Size: 38========= DecompressString ===========Decompress Buffer Size: 662

参考

zlib\src\examples\zpipe.c

C++ Code Snippet - Compressing STL Strings with zlib