compression.hxx

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#include <zlib.h>
#include <string>
 
#include "Exception.hxx"
#include "LOG.hxx"
 
// set buffer chunksize to 65kb
constexpr int CHUNK_SIZE = 65536;
 
std::string compressString(const std::string &stringToCompress)
{
  z_stream zstream;
  std::string compressedString;
  int deflateResult = Z_OK;
  char writeBuffer[CHUNK_SIZE];
 
  // initialize zstream struct with zeroes, to prevent memory access violation during Initialization.
  zstream.zalloc = Z_NULL;
  zstream.zfree = Z_NULL;
  zstream.opaque = Z_NULL;
 
  if (deflateInit(&zstream, Z_BEST_COMPRESSION) != Z_OK)
  {
    if (zstream.msg)
      throw CompressionError(TRACE_INFO "Failed initialize Zlib stream: " + string{zstream.msg});
    throw CompressionError(TRACE_INFO "Failed initialize Zlib stream");
  }
 
  zstream.avail_in = static_cast<unsigned int>(stringToCompress.size());
  zstream.next_in = (Bytef *)stringToCompress.data();
 
  // run decompression until deflate stream ends
  do
  {
    zstream.next_out = reinterpret_cast<Bytef *>(writeBuffer);
    zstream.avail_out = sizeof(writeBuffer);
 
    deflateResult = deflate(&zstream, Z_FINISH);
 
    if (compressedString.size() < zstream.total_out)
    {
      compressedString.append(writeBuffer, zstream.total_out - compressedString.size());
    }
  } while (zstream.avail_out == 0);
 
  deflateEnd(&zstream);
 
  if (deflateResult != Z_STREAM_END)
  {
    if (zstream.msg)
      throw CompressionError(TRACE_INFO "Error while compressing file: " + string{zstream.msg});
    throw CompressionError(TRACE_INFO "Error while compressing file");
  }
 
  return compressedString;
}
 
std::string decompressString(const std::string &compressedString)
{
  z_stream zstream;
  std::string uncompressedString;
  int inflateResult;
  char readBuffer[CHUNK_SIZE];
 
  // initialize zstream struct with zeroes, to prevent memory access violation during Initialization.
  zstream.zalloc = Z_NULL;
  zstream.zfree = Z_NULL;
  zstream.opaque = Z_NULL;
 
  if (inflateInit(&zstream) != Z_OK)
  {
    if (zstream.msg)
      throw CompressionError(TRACE_INFO "Failed initialize Zlib stream: " + string{zstream.msg});
    throw CompressionError(TRACE_INFO "Failed initialize Zlib stream");
  }
 
  zstream.next_in = (Bytef *)compressedString.data();
  zstream.avail_in = static_cast<unsigned int>(compressedString.size());
 
  // run decompression until buffer is empty
  do
  {
    zstream.next_out = reinterpret_cast<Bytef *>(readBuffer);
    zstream.avail_out = sizeof(readBuffer);
 
    inflateResult = inflate(&zstream, 0);
 
    if (uncompressedString.size() < zstream.total_out)
    {
      uncompressedString.append(readBuffer, zstream.total_out - uncompressedString.size());
    }
 
  } while (inflateResult == Z_OK);
 
  inflateEnd(&zstream);
 
  if (inflateResult != Z_STREAM_END)
  {
    if (zstream.msg)
      throw CompressionError(TRACE_INFO "Error while decompressing file: " + string{zstream.msg});
    throw CompressionError(TRACE_INFO "Error while decompressing file");
  }
 
  return uncompressedString;
}