zlib library compression and decompression of the string STL string

zlib library compression and decompression of the string STL string

scenario

1.1 generally, when using text json for data transmission, the process of data transmission is particularly time-consuming, because the bandwidth or the cache of socket is limited, and the larger the data volume, the longer the transmission time will be.

instructions

1.zlib library can achieve gzip and zip compression, here only introduces zip 2-base compression, compression ratio is still considerable, 1 write client program is enough.

2. Modified the implementation of zpipe.c under 1, which is to change the file reading to read string, and the file writing to write string.

example

// test_zlib.cpp :  Define the entry point for the console application. 
//

#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;
}

Output:

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

reference

zlib\src\examples\zpipe.c

C++ Code Snippet - Compressing STL Strings with zlib

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