mariadb/sql/net_serv.cc

/* Copyright (C) 2000 MySQL AB

   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; either version 2 of the License, or
   (at your option) any later version.

   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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/*
  Write and read of logical packets to/from socket

  Writes are cached into net_buffer_length big packets.
  Read packets are reallocated dynamicly when reading big packets.
  Each logical packet has the following pre-info:
  3 byte length & 1 byte package-number.
*/

#ifdef __WIN__
#include <winsock.h>
#endif
#include <my_global.h>
#include <mysql.h>
#include <mysql_embed.h>
#include <mysql_com.h>
#include <mysqld_error.h>
#include <my_sys.h>
#include <m_string.h>
#include <my_net.h>
#include <violite.h>
#include <signal.h>
#include <errno.h>

/*
  The following handles the differences when this is linked between the
  client and the server.

  This gives an error if a too big packet is found
  The server can change this with the -O switch, but because the client
  can't normally do this the client should have a bigger max_allowed_packet.
*/

#ifdef MYSQL_SERVER
#define USE_QUERY_CACHE
extern uint test_flags;
extern void query_cache_insert(NET *net, const char *packet, ulong length);
#else
#endif

#if defined(__WIN__) || !defined(MYSQL_SERVER)
  /* The following is because alarms doesn't work on windows. */
#define NO_ALARM
#endif
  
#ifndef NO_ALARM
#include "my_pthread.h"
void sql_print_error(const char *format,...);
extern ulong bytes_sent, bytes_received;
extern pthread_mutex_t LOCK_bytes_sent , LOCK_bytes_received;
#else
#undef statistic_add
#define statistic_add(A,B,C)
#define DONT_USE_THR_ALARM
#endif /* NO_ALARM */

#include "thr_alarm.h"

#define TEST_BLOCKING		8
#define MAX_THREE_BYTES (256L*256L*256L-1)

static my_bool net_write_buff(NET *net,const char *packet,ulong len);


	/* Init with packet info */

my_bool my_net_init(NET *net, Vio* vio)
{
  DBUG_ENTER("my_net_init");
  my_net_local_init(net);			/* Set some limits */
  if (!(net->buff=(uchar*) my_malloc((uint32) net->max_packet+
				     NET_HEADER_SIZE + COMP_HEADER_SIZE,
				     MYF(MY_WME))))
    DBUG_RETURN(1);
  net->buff_end=net->buff+net->max_packet;
  net->vio = vio;
  net->no_send_ok = 0;
  net->error=0; net->return_errno=0; net->return_status=0;
  net->pkt_nr=net->compress_pkt_nr=0;
  net->write_pos=net->read_pos = net->buff;
  net->last_error[0]=0;
  net->compress=0; net->reading_or_writing=0;
  net->where_b = net->remain_in_buf=0;
  net->last_errno=0;
  net->query_cache_query=0;
  net->report_error= 0;

  if (vio != 0)					/* If real connection */
  {
    net->fd  = vio_fd(vio);			/* For perl DBI/DBD */
#if defined(MYSQL_SERVER) && !defined(___WIN__) && !defined(__EMX__) && !defined(OS2)
    if (!(test_flags & TEST_BLOCKING))
    {
      my_bool old_mode;
      vio_blocking(vio, FALSE, &old_mode);
    }
#endif
    vio_fastsend(vio);
  }
  DBUG_RETURN(0);
}


void net_end(NET *net)
{
  DBUG_ENTER("net_end");
  my_free((gptr) net->buff,MYF(MY_ALLOW_ZERO_PTR));
  net->buff=0;
  DBUG_VOID_RETURN;
}


/* Realloc the packet buffer */

my_bool net_realloc(NET *net, ulong length)
{
  uchar *buff;
  ulong pkt_length;
  if (length >= net->max_packet_size)
  {
    DBUG_PRINT("error",("Packet too large (%lu)", length));
    net->error= 1;
    net->report_error= 1;
    net->last_errno= ER_NET_PACKET_TOO_LARGE;
    return 1;
  }
  pkt_length = (length+IO_SIZE-1) & ~(IO_SIZE-1); 
  /*
    We must allocate some extra bytes for the end 0 and to be able to
    read big compressed blocks
  */
  if (!(buff=(uchar*) my_realloc((char*) net->buff, (uint32) pkt_length +
				 NET_HEADER_SIZE + COMP_HEADER_SIZE,
				 MYF(MY_WME))))
  {
    net->error= 1;
    net->report_error= 1;
#ifdef MYSQL_SERVER
    net->last_errno= ER_OUT_OF_RESOURCES;
#endif
    return 1;
  }
  net->buff=net->write_pos=buff;
  net->buff_end=buff+(net->max_packet=pkt_length);
  return 0;
}

	/* Remove unwanted characters from connection */

void net_clear(NET *net)
{
  DBUG_ENTER("net_clear");
#if !defined(EXTRA_DEBUG) && !defined(EMBEDDED_LIBRARY)
  {
    int count;					/* One may get 'unused' warn */
    my_bool old_mode;
    if (!vio_blocking(net->vio, FALSE, &old_mode))
    {
      while ((count = vio_read(net->vio, (char*) (net->buff),
			       (uint32) net->max_packet)) > 0)
	DBUG_PRINT("info",("skipped %d bytes from file: %s",
			   count, vio_description(net->vio)));
      vio_blocking(net->vio, TRUE, &old_mode);
    }
  }
#endif /* EXTRA_DEBUG */
  net->pkt_nr=net->compress_pkt_nr=0;		/* Ready for new command */
  net->write_pos=net->buff;
  DBUG_VOID_RETURN;
}

	/* Flush write_buffer if not empty. */

my_bool net_flush(NET *net)
{
  my_bool error= 0;
  DBUG_ENTER("net_flush");
  if (net->buff != net->write_pos)
  {
    error=test(net_real_write(net,(char*) net->buff,
			      (ulong) (net->write_pos - net->buff)));
    net->write_pos=net->buff;
  }
  /* Sync packet number if using compression */
  if (net->compress)
    net->pkt_nr=net->compress_pkt_nr;
  DBUG_RETURN(error);
}


/*****************************************************************************
** Write something to server/client buffer
*****************************************************************************/

/*
** Write a logical packet with packet header
** Format: Packet length (3 bytes), packet number(1 byte)
**         When compression is used a 3 byte compression length is added
** NOTE: If compression is used the original package is modified!
*/

my_bool
my_net_write(NET *net,const char *packet,ulong len)
{
  uchar buff[NET_HEADER_SIZE];
  /*
    Big packets are handled by splitting them in packets of MAX_THREE_BYTES
    length. The last packet is always a packet that is < MAX_THREE_BYTES.
    (The last packet may even have a lengt of 0)
  */
  while (len >= MAX_THREE_BYTES)
  {
    const ulong z_size = MAX_THREE_BYTES;
    int3store(buff, z_size);
    buff[3]= (uchar) net->pkt_nr++;
    if (net_write_buff(net, (char*) buff, NET_HEADER_SIZE) ||
	net_write_buff(net, packet, z_size))
      return 1;
    packet += z_size;
    len-=     z_size;
  }
  /* Write last packet */
  int3store(buff,len);
  buff[3]= (uchar) net->pkt_nr++;
  if (net_write_buff(net,(char*) buff,NET_HEADER_SIZE))
    return 1;
  DBUG_DUMP("packet_header",(char*) buff,NET_HEADER_SIZE);
  return net_write_buff(net,packet,len);
}

/*
  Send a command to the server.

  SYNOPSIS
    net_write_command()
    net			NET handler
    command		Command in MySQL server (enum enum_server_command)
    header		Header to write after command
    head_len		Length of header
    packet		Query or parameter to query
    len			Length of packet

  DESCRIPTION
    The reason for having both header and packet is so that libmysql
    can easy add a header to a special command (like prepared statements)
    without having to re-alloc the string.

    As the command is part of the first data packet, we have to do some data
    juggling to put the command in there, without having to create a new
    packet.
    This function will split big packets into sub-packets if needed.
    (Each sub packet can only be 2^24 bytes)

  RETURN VALUES
    0	ok
    1	error
*/

my_bool
net_write_command(NET *net,uchar command,
		  const char *header, ulong head_len,
		  const char *packet, ulong len)
{
  ulong length=len+1+head_len;			/* 1 extra byte for command */
  uchar buff[NET_HEADER_SIZE+1];
  uint header_size=NET_HEADER_SIZE+1;
  buff[4]=command;				/* For first packet */

  if (length >= MAX_THREE_BYTES)
  {
    /* Take into account that we have the command in the first header */
    len= MAX_THREE_BYTES - 1 - head_len;
    do
    {
      int3store(buff, MAX_THREE_BYTES);
      buff[3]= (uchar) net->pkt_nr++;
      if (net_write_buff(net,(char*) buff, header_size) ||
	  net_write_buff(net, header, head_len) ||
	  net_write_buff(net, packet, len))
	return 1;
      packet+= len;
      length-= MAX_THREE_BYTES;
      len=MAX_THREE_BYTES;
      head_len=0;
      header_size=NET_HEADER_SIZE;
    } while (length >= MAX_THREE_BYTES);
    len=length;					/* Data left to be written */
  }
  int3store(buff,length);
  buff[3]= (uchar) net->pkt_nr++;
  return test(net_write_buff(net, (char*) buff, header_size) ||
	      (head_len && net_write_buff(net, (char*) header, head_len)) ||
	      net_write_buff(net, packet, len) || net_flush(net));
}

/*
  Caching the data in a local buffer before sending it.
  One can force the buffer to be flushed with 'net_flush'.

*/

static my_bool
net_write_buff(NET *net,const char *packet,ulong len)
{
  ulong left_length=(ulong) (net->buff_end - net->write_pos);

  if (len > left_length)
  {
    memcpy((char*) net->write_pos,packet,left_length);
    if (net_real_write(net,(char*) net->buff,net->max_packet))
      return 1;
    net->write_pos=net->buff;
    packet+=left_length;
    len-= left_length;
    left_length= net->max_packet;

    /* Send out rest of the blocks as full sized blocks */
    while (len > left_length)
    {
      if (net_real_write(net, packet, left_length))
	return 1;
      packet+= left_length;
      len-= left_length;
    }
  }
  memcpy((char*) net->write_pos,packet,len);
  net->write_pos+=len;
  return 0;
}


/*
  Read and write one packet using timeouts.
  If needed, the packet is compressed before sending.
*/

int
net_real_write(NET *net,const char *packet,ulong len)
{
  long int length;
  char *pos,*end;
  thr_alarm_t alarmed;
#ifndef NO_ALARM
  ALARM alarm_buff;
#endif
  uint retry_count=0;
  my_bool net_blocking = vio_is_blocking(net->vio);
  DBUG_ENTER("net_real_write");

#if defined(MYSQL_SERVER) && defined(HAVE_QUERY_CACHE)
  if (net->query_cache_query != 0)
    query_cache_insert(net, packet, len);
#endif

  if (net->error == 2)
    DBUG_RETURN(-1);				/* socket can't be used */

  net->reading_or_writing=2;
#ifdef HAVE_COMPRESS
  if (net->compress)
  {
    ulong complen;
    uchar *b;
    uint header_length=NET_HEADER_SIZE+COMP_HEADER_SIZE;
    if (!(b=(uchar*) my_malloc((uint32) len + NET_HEADER_SIZE +
			       COMP_HEADER_SIZE, MYF(MY_WME))))
    {
#ifdef MYSQL_SERVER
      net->last_errno= ER_OUT_OF_RESOURCES;
      net->error= 2;
      //TODO is it needed to set this variable if we have no socket
      net->report_error= 1;
#endif
      net->reading_or_writing= 0;
      DBUG_RETURN(1);
    }
    memcpy(b+header_length,packet,len);

    if (my_compress((byte*) b+header_length,&len,&complen))
    {
      DBUG_PRINT("warning",
		 ("Compression error; Continuing without compression"));
      complen=0;
    }
    int3store(&b[NET_HEADER_SIZE],complen);
    int3store(b,len);
    b[3]=(uchar) (net->compress_pkt_nr++);
    len+= header_length;
    packet= (char*) b;
  }
#endif /* HAVE_COMPRESS */

  /* DBUG_DUMP("net",packet,len); */
#ifndef NO_ALARM
  thr_alarm_init(&alarmed);
  if (net_blocking)
    thr_alarm(&alarmed,(uint) net->write_timeout,&alarm_buff);
#else
  alarmed=0;
#endif /* NO_ALARM */

  pos=(char*) packet; end=pos+len;
  while (pos != end)
  {
    if ((long) (length=vio_write(net->vio,pos,(uint32) (end-pos))) <= 0)
    {
      my_bool interrupted = vio_should_retry(net->vio);
#if (!defined(__WIN__) && !defined(__EMX__) && !defined(OS2))
      if ((interrupted || length==0) && !thr_alarm_in_use(&alarmed))
      {
        if (!thr_alarm(&alarmed,(uint) net->write_timeout,&alarm_buff))
        {                                       /* Always true for client */
	  my_bool old_mode;
	  while (vio_blocking(net->vio, TRUE, &old_mode) < 0)
	  {
	    if (vio_should_retry(net->vio) && retry_count++ < net->retry_count)
	      continue;
#ifdef EXTRA_DEBUG
	    fprintf(stderr,
		    "%s: my_net_write: fcntl returned error %d, aborting thread\n",
		    my_progname,vio_errno(net->vio));
#endif /* EXTRA_DEBUG */
#ifdef MYSQL_SERVER	    
	    net->last_errno= ER_NET_ERROR_ON_WRITE;
#endif
	    net->error= 2;                     /* Close socket */
            net->report_error= 1;
	    goto end;
	  }
	  retry_count=0;
	  continue;
	}
      }
      else
#endif /* (!defined(__WIN__) && !defined(__EMX__)) */
	if (thr_alarm_in_use(&alarmed) && !thr_got_alarm(&alarmed) &&
	    interrupted)
      {
	if (retry_count++ < net->retry_count)
	    continue;
#ifdef EXTRA_DEBUG
	  fprintf(stderr, "%s: write looped, aborting thread\n",
		  my_progname);
#endif /* EXTRA_DEBUG */
      }
#if defined(THREAD_SAFE_CLIENT) && !defined(MYSQL_SERVER)
      if (vio_errno(net->vio) == SOCKET_EINTR)
      {
	DBUG_PRINT("warning",("Interrupted write. Retrying..."));
	continue;
      }
#endif /* defined(THREAD_SAFE_CLIENT) && !defined(MYSQL_SERVER) */
      net->error= 2;				/* Close socket */
      net->report_error= 1;
#ifdef MYSQL_SERVER
      net->last_errno= (interrupted ? ER_NET_WRITE_INTERRUPTED :
			ER_NET_ERROR_ON_WRITE);
#endif /* MYSQL_SERVER */
      break;
    }
    pos+=length;
    statistic_add(bytes_sent,length,&LOCK_bytes_sent);
  }
#ifndef __WIN__
 end:
#endif
#ifdef HAVE_COMPRESS
  if (net->compress)
    my_free((char*) packet,MYF(0));
#endif
  if (thr_alarm_in_use(&alarmed))
  {
    my_bool old_mode;
    thr_end_alarm(&alarmed);
    vio_blocking(net->vio, net_blocking, &old_mode);
  }
  net->reading_or_writing=0;
  DBUG_RETURN(((int) (pos != end)));
}


/*****************************************************************************
** Read something from server/clinet
*****************************************************************************/

#ifndef NO_ALARM
/*
  Help function to clear the commuication buffer when we get a too
  big packet
*/

static void my_net_skip_rest(NET *net, uint32 remain, thr_alarm_t *alarmed)
{
  ALARM alarm_buff;
  uint retry_count=0;
  my_bool old_mode;
  uint32 old=remain;

  if (!thr_alarm_in_use(&alarmed))
  {
    if (!thr_alarm(alarmed,net->read_timeout,&alarm_buff) ||
	vio_blocking(net->vio, TRUE, &old_mode) < 0)
      return;					/* Can't setup, abort */
  }
  while (remain > 0)
  {
    ulong length;
    if ((int) (length=vio_read(net->vio,(char*) net->buff,remain)) <= 0L)
    {
      my_bool interrupted = vio_should_retry(net->vio);
      if (!thr_got_alarm(&alarmed) && interrupted)
      {					/* Probably in MIT threads */
	if (retry_count++ < net->retry_count)
	  continue;
      }
      return;
    }
    remain -= (uint32) length;
    if (!remain && old==MAX_THREE_BYTES && 
	(length=vio_read(net->vio,(char*) net->buff,NET_HEADER_SIZE)))
    {
      old=remain= uint3korr(net->buff);
      net->pkt_nr++;
    }
    statistic_add(bytes_received,length,&LOCK_bytes_received);
  }
}
#endif /* NO_ALARM */


/*
  Reads one packet to net->buff + net->where_b
  Returns length of packet.  Long packets are handled by my_net_read().
  This function reallocates the net->buff buffer if necessary.
*/

static ulong
my_real_read(NET *net, ulong *complen)
{
  uchar *pos;
  long length;
  uint i,retry_count=0;
  ulong len=packet_error;
  thr_alarm_t alarmed;
#ifndef NO_ALARM
  ALARM alarm_buff;
#endif
  my_bool net_blocking=vio_is_blocking(net->vio);
  uint32 remain= (net->compress ? NET_HEADER_SIZE+COMP_HEADER_SIZE :
		  NET_HEADER_SIZE);
  *complen = 0;

  net->reading_or_writing=1;
  thr_alarm_init(&alarmed);
#ifndef NO_ALARM
  if (net_blocking)
    thr_alarm(&alarmed,net->read_timeout,&alarm_buff);
#endif /* NO_ALARM */

    pos = net->buff + net->where_b;		/* net->packet -4 */
    for (i=0 ; i < 2 ; i++)
    {
      while (remain > 0)
      {
	/* First read is done with non blocking mode */
        if ((int) (length=vio_read(net->vio,(char*) pos,remain)) <= 0L)
        {
          my_bool interrupted = vio_should_retry(net->vio);

	  DBUG_PRINT("info",("vio_read returned %d,  errno: %d",
			     length, vio_errno(net->vio)));
#if (!defined(__WIN__) && !defined(__EMX__) && !defined(OS2)) || defined(MYSQL_SERVER)
	  /*
	    We got an error that there was no data on the socket. We now set up
	    an alarm to not 'read forever', change the socket to non blocking
	    mode and try again
	  */
	  if ((interrupted || length == 0) && !thr_alarm_in_use(&alarmed))
	  {
	    if (!thr_alarm(&alarmed,net->read_timeout,&alarm_buff)) /* Don't wait too long */
	    {
	      my_bool old_mode;
	      while (vio_blocking(net->vio, TRUE, &old_mode) < 0)
	      {
		if (vio_should_retry(net->vio) &&
		    retry_count++ < net->retry_count)
		  continue;
		DBUG_PRINT("error",
			   ("fcntl returned error %d, aborting thread",
			    vio_errno(net->vio)));
#ifdef EXTRA_DEBUG
		fprintf(stderr,
			"%s: read: fcntl returned error %d, aborting thread\n",
			my_progname,vio_errno(net->vio));
#endif /* EXTRA_DEBUG */
		len= packet_error;
		net->error= 2;                 /* Close socket */
	        net->report_error= 1;
#ifdef MYSQL_SERVER
		net->last_errno= ER_NET_FCNTL_ERROR;
#endif
		goto end;
	      }
	      retry_count=0;
	      continue;
	    }
	  }
#endif /* (!defined(__WIN__) && !defined(__EMX__)) || defined(MYSQL_SERVER) */
	  if (thr_alarm_in_use(&alarmed) && !thr_got_alarm(&alarmed) &&
	      interrupted)
	  {					/* Probably in MIT threads */
	    if (retry_count++ < net->retry_count)
	      continue;
#ifdef EXTRA_DEBUG
	    fprintf(stderr, "%s: read looped with error %d, aborting thread\n",
		    my_progname,vio_errno(net->vio));
#endif /* EXTRA_DEBUG */
	  }
#if defined(THREAD_SAFE_CLIENT) && !defined(MYSQL_SERVER)
	  if (vio_should_retry(net->vio))
	  {
	    DBUG_PRINT("warning",("Interrupted read. Retrying..."));
	    continue;
	  }
#endif
	  DBUG_PRINT("error",("Couldn't read packet: remain: %lu  errno: %d  length: %ld  alarmed: %d",
			      remain,vio_errno(net->vio), length,
			      thr_got_alarm(&alarmed)));
	  len= packet_error;
	  net->error= 2;				/* Close socket */
	  net->report_error= 1;
#ifdef MYSQL_SERVER
	  net->last_errno= (interrupted ? ER_NET_READ_INTERRUPTED :
			    ER_NET_READ_ERROR);
#endif
	  goto end;
	}
	remain -= (uint32) length;
	pos+= (ulong) length;
	statistic_add(bytes_received,(ulong) length,&LOCK_bytes_received);
      }
      if (i == 0)
      {					/* First parts is packet length */
	ulong helping;
	if (net->buff[net->where_b + 3] != (uchar) net->pkt_nr)
	{
	  if (net->buff[net->where_b] != (uchar) 255)
	  {
	    DBUG_PRINT("error",
		       ("Packets out of order (Found: %d, expected %u)",
			(int) net->buff[net->where_b + 3],
			net->pkt_nr));
	    DBUG_DUMP("packet_header",(char*) net->buff+net->where_b, 4);
#ifdef EXTRA_DEBUG
	    fprintf(stderr,"Packets out of order (Found: %d, expected %d)\n",
		    (int) net->buff[net->where_b + 3],
		    (uint) (uchar) net->pkt_nr);
#endif
	  }
	  len= packet_error;
	  net->report_error= 1;
#ifdef MYSQL_SERVER
	  net->last_errno=ER_NET_PACKETS_OUT_OF_ORDER;
#endif
	  goto end;
	}
	net->compress_pkt_nr= ++net->pkt_nr;
#ifdef HAVE_COMPRESS
	if (net->compress)
	{
	  /*
	    If the packet is compressed then complen > 0 and contains the
	    number of bytes in the uncompressed packet
	  */
	  *complen=uint3korr(&(net->buff[net->where_b + NET_HEADER_SIZE]));
	}
#endif

	len=uint3korr(net->buff+net->where_b);
	if (!len)				/* End of big multi-packet */
	  goto end;
	helping = max(len,*complen) + net->where_b;
	/* The necessary size of net->buff */
	if (helping >= net->max_packet)
	{
	  if (net_realloc(net,helping))
	  {
#ifdef MYSQL_SERVER
#ifndef NO_ALARM
	    if (net->compress)
	    {
	      len= packet_error;
	      goto end;
	    }
	    my_net_skip_rest(net, (uint32) len, &alarmed);
	    len=0;
#endif
#else
	    len= packet_error;          /* Return error */
#endif
	    goto end;
	  }
	}
	pos=net->buff + net->where_b;
	remain = (uint32) len;
      }
    }

end:
  if (thr_alarm_in_use(&alarmed))
  {
    my_bool old_mode;
    thr_end_alarm(&alarmed);
    vio_blocking(net->vio, net_blocking, &old_mode);
  }
  net->reading_or_writing=0;
  return(len);
}


/*
  Read a packet from the client/server and return it without the internal
  package header.
  If the packet is the first packet of a multi-packet packet
  (which is indicated by the length of the packet = 0xffffff) then
  all sub packets are read and concatenated.
  If the packet was compressed, its uncompressed and the length of the
  uncompressed packet is returned.

  The function returns the length of the found packet or packet_error.
  net->read_pos points to the read data.
*/

ulong
my_net_read(NET *net)
{
  ulong len,complen;

#ifdef HAVE_COMPRESS
  if (!net->compress)
  {
#endif
    len = my_real_read(net,&complen);
    if (len == MAX_THREE_BYTES)
    {
      /* First packet of a multi-packet.  Concatenate the packets */
      ulong save_pos = net->where_b;
      ulong total_length=0;
      do
      {
	net->where_b += len;
	total_length += len;
	len = my_real_read(net,&complen);
      } while (len == MAX_THREE_BYTES);
      if (len != packet_error)
	len+= total_length;
      net->where_b = save_pos;
    }
    net->read_pos = net->buff + net->where_b;
    if (len != packet_error)
      net->read_pos[len]=0;		/* Safeguard for mysql_use_result */
    return len;
#ifdef HAVE_COMPRESS
  }
  else
  {
    /* We are using the compressed protocol */

    ulong buf_length=       net->buf_length;
    ulong start_of_packet=  net->buf_length - net->remain_in_buf;
    ulong first_packet_offset=start_of_packet;
    uint read_length, multi_byte_packet=0;

    if (net->remain_in_buf)
    {
      /* Restore the character that was overwritten by the end 0 */
      net->buff[start_of_packet]=net->save_char;
    }
    else
    {
      /* reuse buffer, as there is nothing in it that we need */
      buf_length=start_of_packet=first_packet_offset=0;
    }
    for (;;)
    {
      ulong packet_len;

      if (buf_length - start_of_packet >= NET_HEADER_SIZE)
      {
	read_length = uint3korr(net->buff+start_of_packet);
	if (!read_length)
	{ 
	  /* End of multi-byte packet */
	  start_of_packet += NET_HEADER_SIZE;
	  break;
	}
	if (read_length + NET_HEADER_SIZE <= buf_length - start_of_packet)
	{
	  if (multi_byte_packet)
	  {
	    /* Remove packet header for second packet */
	    memmove(net->buff + first_packet_offset + start_of_packet,
		    net->buff + first_packet_offset + start_of_packet +
		    NET_HEADER_SIZE,
		    buf_length - start_of_packet);
	    start_of_packet += read_length;
	    buf_length -= NET_HEADER_SIZE;
	  }
	  else
	    start_of_packet+= read_length + NET_HEADER_SIZE;

	  if (read_length != MAX_THREE_BYTES)	    /* last package */
	  {
	    multi_byte_packet= 0;		/* No last zero len packet */
	    break;
	  }
	  multi_byte_packet= NET_HEADER_SIZE;
	  /* Move data down to read next data packet after current one */
	  if (first_packet_offset)
	  {
	    memmove(net->buff,net->buff+first_packet_offset,
		    buf_length-first_packet_offset);
	    buf_length-=first_packet_offset;
	    start_of_packet -= first_packet_offset;
	    first_packet_offset=0;
	  }
	  continue;
	}
      }
      /* Move data down to read next data packet after current one */
      if (first_packet_offset)
      {
	memmove(net->buff,net->buff+first_packet_offset,
		buf_length-first_packet_offset);
	buf_length-=first_packet_offset;
	start_of_packet -= first_packet_offset;
	first_packet_offset=0;
      }

      net->where_b=buf_length;
      if ((packet_len = my_real_read(net,&complen)) == packet_error)
	return packet_error;
      if (my_uncompress((byte*) net->buff + net->where_b, &packet_len,
			&complen))
      {
	net->error= 2;			/* caller will close socket */
	net->report_error= 1;
#ifdef MYSQL_SERVER
	net->last_errno=ER_NET_UNCOMPRESS_ERROR;
#endif
	return packet_error;
      }
      buf_length+=packet_len;
    }

    net->read_pos=      net->buff+ first_packet_offset + NET_HEADER_SIZE;
    net->buf_length=    buf_length;
    net->remain_in_buf= (ulong) (buf_length - start_of_packet);
    len = ((ulong) (start_of_packet - first_packet_offset) - NET_HEADER_SIZE -
           multi_byte_packet);
    net->save_char= net->read_pos[len];	/* Must be saved */
    net->read_pos[len]=0;		/* Safeguard for mysql_use_result */
  }
#endif /* HAVE_COMPRESS */
  return len;
}