/* Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */

/* Written by Sinisa Milivojevic <sinisa@mysql.com> */

#include <mysys_priv.h>
#ifdef HAVE_COMPRESS
#include <my_sys.h>
#ifndef SCO
#include <m_string.h>
#endif
#include <zlib.h>

/*
   This replaces the packet with a compressed packet

   SYNOPSIS
     my_compress()
     packet	Data to compress. This is is replaced with the compressed data.
     len	Length of data to compress at 'packet'
     complen	out: 0 if packet was not compressed

   RETURN
     1   error. 'len' is not changed'
     0   ok.  In this case 'len' contains the size of the compressed packet
*/

my_bool my_compress(uchar *packet, size_t *len, size_t *complen)
{
  DBUG_ENTER("my_compress");
  if (*len < MIN_COMPRESS_LENGTH)
  {
    *complen=0;
    DBUG_PRINT("note",("Packet too short: Not compressed"));
  }
  else
  {
    uchar *compbuf=my_compress_alloc(packet,len,complen);
    if (!compbuf)
      DBUG_RETURN(*complen ? 0 : 1);
    memcpy(packet,compbuf,*len);
    my_free(compbuf);
  }
  DBUG_RETURN(0);
}


/*
  Valgrind normally gives false alarms for zlib operations, in the form of
  "conditional jump depends on uninitialised values" etc. The reason is
  explained in the zlib FAQ (http://www.zlib.net/zlib_faq.html#faq36):

    "That is intentional for performance reasons, and the output of deflate
    is not affected."

  Also discussed on a blog
  (http://www.sirena.org.uk/log/2006/02/19/zlib-generating-valgrind-warnings/):

    "...loop unrolling in the zlib library causes the mentioned
    “Conditional jump or move depends on uninitialised value(s)”
    warnings. These are safe since the results of the comparison are
    subsequently ignored..."

    "the results of the calculations are discarded by bounds checking done
    after the loop exits"

  Fix by initializing the memory allocated by zlib when running under Valgrind.

  This fix is safe, since such memory is only used internally by zlib, so we
  will not hide any bugs in mysql this way.
*/
void *my_az_allocator(void *dummy __attribute__((unused)), unsigned int items,
                      unsigned int size)
{
  return my_malloc(key_memory_my_compress_alloc, (size_t)items*(size_t)size,
                   IF_VALGRIND(MY_ZEROFILL, MYF(0)));
}

void my_az_free(void *dummy __attribute__((unused)), void *address)
{
  my_free(address);
}

/*
  This works like zlib compress(), but using custom memory allocators to work
  better with my_malloc leak detection and Valgrind.
*/
int my_compress_buffer(uchar *dest, size_t *destLen,
                       const uchar *source, size_t sourceLen)
{
    z_stream stream;
    int err;

    stream.next_in = (Bytef*)source;
    stream.avail_in = (uInt)sourceLen;
    stream.next_out = (Bytef*)dest;
    stream.avail_out = (uInt)*destLen;
    if ((size_t)stream.avail_out != *destLen)
      return Z_BUF_ERROR;

    stream.zalloc = (alloc_func)my_az_allocator;
    stream.zfree = (free_func)my_az_free;
    stream.opaque = (voidpf)0;

    err = deflateInit(&stream, Z_DEFAULT_COMPRESSION);
    if (err != Z_OK) return err;

    err = deflate(&stream, Z_FINISH);
    if (err != Z_STREAM_END) {
        deflateEnd(&stream);
        return err == Z_OK ? Z_BUF_ERROR : err;
    }
    *destLen = stream.total_out;

    err = deflateEnd(&stream);
    return err;
}

uchar *my_compress_alloc(const uchar *packet, size_t *len, size_t *complen)
{
  uchar *compbuf;
  int res;
  *complen=  *len * 120 / 100 + 12;

  if (!(compbuf= (uchar *) my_malloc(key_memory_my_compress_alloc,
                                     *complen, MYF(MY_WME))))
    return 0;

  res= my_compress_buffer(compbuf, complen, packet, *len);

  if (res != Z_OK)
  {
    my_free(compbuf);
    return 0;
  }

  if (*complen >= *len)
  {
    *complen= 0;
    my_free(compbuf);
    DBUG_PRINT("note",("Packet got longer on compression; Not compressed"));
    return 0;
  }
  /* Store length of compressed packet in *len */
  swap_variables(size_t, *len, *complen);
  return compbuf;
}


/*
  Uncompress packet

   SYNOPSIS
     my_uncompress()
     packet	Compressed data. This is is replaced with the original data.
     len	Length of compressed data
     complen	Length of the packet buffer (must be enough for the original
	        data)

   RETURN
     1   error
     0   ok.  In this case 'complen' contains the updated size of the
              real data.
*/

my_bool my_uncompress(uchar *packet, size_t len, size_t *complen)
{
  uLongf tmp_complen;
  DBUG_ENTER("my_uncompress");

  if (*complen)					/* If compressed */
  {
    uchar *compbuf= (uchar *) my_malloc(key_memory_my_compress_alloc,
                                        *complen,MYF(MY_WME));
    int error;
    if (!compbuf)
      DBUG_RETURN(1);				/* Not enough memory */

    tmp_complen= (uLongf) *complen;
    error= uncompress((Bytef*) compbuf, &tmp_complen, (Bytef*) packet,
                      (uLong) len);
    *complen= tmp_complen;
    if (error != Z_OK)
    {						/* Probably wrong packet */
      DBUG_PRINT("error",("Can't uncompress packet, error: %d",error));
      my_free(compbuf);
      DBUG_RETURN(1);
    }
    memcpy(packet, compbuf, *complen);
    my_free(compbuf);
  }
  else
    *complen= len;
  DBUG_RETURN(0);
}

#endif /* HAVE_COMPRESS */
