zlib库压缩和解压字符串STL string的实例详解

zlib库压缩和解压字符串STL string的实例详解

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

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