mariadb/sql/sql_error.cc

/* Copyright (C) 1995-2002 MySQL AB,
   Copyright (C) 2008-2009 Sun Microsystems, Inc

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

/**********************************************************************
This file contains the implementation of error and warnings related

  - Whenever an error or warning occurred, it pushes it to a warning list
    that the user can retrieve with SHOW WARNINGS or SHOW ERRORS.

  - For each statement, we return the number of warnings generated from this
    command.  Note that this can be different from @@warning_count as
    we reset the warning list only for questions that uses a table.
    This is done to allow on to do:
    INSERT ...;
    SELECT @@warning_count;
    SHOW WARNINGS;
    (If we would reset after each command, we could not retrieve the number
     of warnings)

  - When client requests the information using SHOW command, then 
    server processes from this list and returns back in the form of 
    resultset.

    Supported syntaxes:

    SHOW [COUNT(*)] ERRORS [LIMIT [offset,] rows]
    SHOW [COUNT(*)] WARNINGS [LIMIT [offset,] rows]
    SELECT @@warning_count, @@error_count;

***********************************************************************/

#include "sql_priv.h"
#include "unireg.h"
#include "sql_error.h"
#include "sp_rcontext.h"

/*
  Design notes about MYSQL_ERROR::m_message_text.

  The member MYSQL_ERROR::m_message_text contains the text associated with
  an error, warning or note (which are all SQL 'conditions')

  Producer of MYSQL_ERROR::m_message_text:
  ----------------------------------------

  (#1) the server implementation itself, when invoking functions like
  my_error() or push_warning()

  (#2) user code in stored programs, when using the SIGNAL statement.

  (#3) user code in stored programs, when using the RESIGNAL statement.

  When invoking my_error(), the error number and message is typically
  provided like this:
  - my_error(ER_WRONG_DB_NAME, MYF(0), ...);
  - my_message(ER_SLAVE_IGNORED_TABLE, ER(ER_SLAVE_IGNORED_TABLE), MYF(0));

  In both cases, the message is retrieved from ER(ER_XXX), which in turn
  is read from the resource file errmsg.sys at server startup.
  The strings stored in the errmsg.sys file are expressed in the character set
  that corresponds to the server --language start option
  (see error_message_charset_info).

  When executing:
  - a SIGNAL statement,
  - a RESIGNAL statement,
  the message text is provided by the user logic, and is expressed in UTF8.

  Storage of MYSQL_ERROR::m_message_text:
  ---------------------------------------

  (#4) The class MYSQL_ERROR is used to hold the message text member.
  This class represents a single SQL condition.

  (#5) The class Warning_info represents a SQL condition area, and contains
  a collection of SQL conditions in the Warning_info::m_warn_list

  Consumer of MYSQL_ERROR::m_message_text:
  ----------------------------------------

  (#6) The statements SHOW WARNINGS and SHOW ERRORS display the content of
  the warning list.

  (#7) The GET DIAGNOSTICS statement (planned, not implemented yet) will
  also read the content of:
  - the top level statement condition area (when executed in a query),
  - a sub statement (when executed in a stored program)
  and return the data stored in a MYSQL_ERROR.

  (#8) The RESIGNAL statement reads the MYSQL_ERROR caught by an exception
  handler, to raise a new or modified condition (in #3).

  The big picture
  ---------------
                                                              --------------
                                                              |            ^
                                                              V            |
  my_error(#1)                 SIGNAL(#2)                 RESIGNAL(#3)     |
      |(#A)                       |(#B)                       |(#C)        |
      |                           |                           |            |
      ----------------------------|----------------------------            |
                                  |                                        |
                                  V                                        |
                           MYSQL_ERROR(#4)                                 |
                                  |                                        |
                                  |                                        |
                                  V                                        |
                           Warning_info(#5)                                |
                                  |                                        |
          -----------------------------------------------------            |
          |                       |                           |            |
          |                       |                           |            |
          |                       |                           |            |
          V                       V                           V            |
   SHOW WARNINGS(#6)      GET DIAGNOSTICS(#7)              RESIGNAL(#8)    |
          |  |                    |                           |            |
          |  --------             |                           V            |
          |         |             |                           --------------
          V         |             |
      Connectors    |             |
          |         |             |
          -------------------------
                    |
                    V
             Client application

  Current implementation status
  -----------------------------

  (#1) (my_error) produces data in the 'error_message_charset_info' CHARSET

  (#2) and (#3) (SIGNAL, RESIGNAL) produces data internally in UTF8

  (#6) (SHOW WARNINGS) produces data in the 'error_message_charset_info' CHARSET

  (#7) (GET DIAGNOSTICS) is not implemented.

  (#8) (RESIGNAL) produces data internally in UTF8 (see #3)

  As a result, the design choice for (#4) and (#5) is to store data in
  the 'error_message_charset_info' CHARSET, to minimize impact on the code base.
  This is implemented by using 'String MYSQL_ERROR::m_message_text'.

  The UTF8 -> error_message_charset_info conversion is implemented in
  Signal_common::eval_signal_informations() (for path #B and #C).

  Future work
  -----------

  - Change (#1) (my_error) to generate errors in UTF8.
    See WL#751 (Recoding of error messages)

  - Change (#4 and #5) to store message text in UTF8 natively.
    In practice, this means changing the type of the message text to
    '<UTF8 String 128 class> MYSQL_ERROR::m_message_text', and is a direct
    consequence of WL#751.

  - Implement (#9) (GET DIAGNOSTICS).
    See WL#2111 (Stored Procedures: Implement GET DIAGNOSTICS)
*/

MYSQL_ERROR::MYSQL_ERROR()
 : Sql_alloc(),
   m_class_origin((const char*) NULL, 0, & my_charset_utf8_bin),
   m_subclass_origin((const char*) NULL, 0, & my_charset_utf8_bin),
   m_constraint_catalog((const char*) NULL, 0, & my_charset_utf8_bin),
   m_constraint_schema((const char*) NULL, 0, & my_charset_utf8_bin),
   m_constraint_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_catalog_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_schema_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_table_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_column_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_cursor_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_message_text(),
   m_sql_errno(0),
   m_level(MYSQL_ERROR::WARN_LEVEL_ERROR),
   m_mem_root(NULL)
{
  memset(m_returned_sqlstate, 0, sizeof(m_returned_sqlstate));
}

void MYSQL_ERROR::init(MEM_ROOT *mem_root)
{
  DBUG_ASSERT(mem_root != NULL);
  DBUG_ASSERT(m_mem_root == NULL);
  m_mem_root= mem_root;
}

void MYSQL_ERROR::clear()
{
  m_class_origin.length(0);
  m_subclass_origin.length(0);
  m_constraint_catalog.length(0);
  m_constraint_schema.length(0);
  m_constraint_name.length(0);
  m_catalog_name.length(0);
  m_schema_name.length(0);
  m_table_name.length(0);
  m_column_name.length(0);
  m_cursor_name.length(0);
  m_message_text.length(0);
  m_sql_errno= 0;
  m_level= MYSQL_ERROR::WARN_LEVEL_ERROR;
}

MYSQL_ERROR::MYSQL_ERROR(MEM_ROOT *mem_root)
 : Sql_alloc(),
   m_class_origin((const char*) NULL, 0, & my_charset_utf8_bin),
   m_subclass_origin((const char*) NULL, 0, & my_charset_utf8_bin),
   m_constraint_catalog((const char*) NULL, 0, & my_charset_utf8_bin),
   m_constraint_schema((const char*) NULL, 0, & my_charset_utf8_bin),
   m_constraint_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_catalog_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_schema_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_table_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_column_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_cursor_name((const char*) NULL, 0, & my_charset_utf8_bin),
   m_message_text(),
   m_sql_errno(0),
   m_level(MYSQL_ERROR::WARN_LEVEL_ERROR),
   m_mem_root(mem_root)
{
  DBUG_ASSERT(mem_root != NULL);
  memset(m_returned_sqlstate, 0, sizeof(m_returned_sqlstate));
}

static void copy_string(MEM_ROOT *mem_root, String* dst, const String* src)
{
  size_t len= src->length();
  if (len)
  {
    char* copy= (char*) alloc_root(mem_root, len + 1);
    if (copy)
    {
      memcpy(copy, src->ptr(), len);
      copy[len]= '\0';
      dst->set(copy, len, src->charset());
    }
  }
  else
    dst->length(0);
}

void
MYSQL_ERROR::copy_opt_attributes(const MYSQL_ERROR *cond)
{
  DBUG_ASSERT(this != cond);
  copy_string(m_mem_root, & m_class_origin, & cond->m_class_origin);
  copy_string(m_mem_root, & m_subclass_origin, & cond->m_subclass_origin);
  copy_string(m_mem_root, & m_constraint_catalog, & cond->m_constraint_catalog);
  copy_string(m_mem_root, & m_constraint_schema, & cond->m_constraint_schema);
  copy_string(m_mem_root, & m_constraint_name, & cond->m_constraint_name);
  copy_string(m_mem_root, & m_catalog_name, & cond->m_catalog_name);
  copy_string(m_mem_root, & m_schema_name, & cond->m_schema_name);
  copy_string(m_mem_root, & m_table_name, & cond->m_table_name);
  copy_string(m_mem_root, & m_column_name, & cond->m_column_name);
  copy_string(m_mem_root, & m_cursor_name, & cond->m_cursor_name);
}

void
MYSQL_ERROR::set(uint sql_errno, const char* sqlstate,
                 MYSQL_ERROR::enum_warning_level level, const char* msg)
{
  DBUG_ASSERT(sql_errno != 0);
  DBUG_ASSERT(sqlstate != NULL);
  DBUG_ASSERT(msg != NULL);

  m_sql_errno= sql_errno;
  memcpy(m_returned_sqlstate, sqlstate, SQLSTATE_LENGTH);
  m_returned_sqlstate[SQLSTATE_LENGTH]= '\0';

  set_builtin_message_text(msg);
  m_level= level;
}

void
MYSQL_ERROR::set_builtin_message_text(const char* str)
{
  /*
    See the comments
     "Design notes about MYSQL_ERROR::m_message_text."
  */
  const char* copy;

  copy= strdup_root(m_mem_root, str);
  m_message_text.set(copy, strlen(copy), error_message_charset_info);
  DBUG_ASSERT(! m_message_text.is_alloced());
}

const char*
MYSQL_ERROR::get_message_text() const
{
  return m_message_text.ptr();
}

int
MYSQL_ERROR::get_message_octet_length() const
{
  return m_message_text.length();
}

void
MYSQL_ERROR::set_sqlstate(const char* sqlstate)
{
  memcpy(m_returned_sqlstate, sqlstate, SQLSTATE_LENGTH);
  m_returned_sqlstate[SQLSTATE_LENGTH]= '\0';
}

/**
  Clear this diagnostics area.

  Normally called at the end of a statement.
*/

void
Diagnostics_area::reset_diagnostics_area()
{
  DBUG_ENTER("reset_diagnostics_area");
#ifdef DBUG_OFF
  can_overwrite_status= FALSE;
  /** Don't take chances in production */
  m_message[0]= '\0';
  m_sql_errno= 0;
  m_server_status= 0;
  m_affected_rows= 0;
  m_last_insert_id= 0;
  m_statement_warn_count= 0;
#endif
  is_sent= FALSE;
  /** Tiny reset in debug mode to see garbage right away */
  m_status= DA_EMPTY;
  DBUG_VOID_RETURN;
}


/**
  Set OK status -- ends commands that do not return a
  result set, e.g. INSERT/UPDATE/DELETE.
*/

void
Diagnostics_area::set_ok_status(THD *thd, ulonglong affected_rows_arg,
                                ulonglong last_insert_id_arg,
                                const char *message_arg)
{
  DBUG_ENTER("set_ok_status");
  DBUG_ASSERT(! is_set());
  /*
    In production, refuse to overwrite an error or a custom response
    with an OK packet.
  */
  if (is_error() || is_disabled())
    return;

  m_statement_warn_count= thd->warning_info->statement_warn_count();
  m_affected_rows= affected_rows_arg;
  m_last_insert_id= last_insert_id_arg;
  if (message_arg)
    strmake(m_message, message_arg, sizeof(m_message) - 1);
  else
    m_message[0]= '\0';
  m_status= DA_OK;
  DBUG_VOID_RETURN;
}


/**
  Set EOF status.
*/

void
Diagnostics_area::set_eof_status(THD *thd)
{
  DBUG_ENTER("set_eof_status");
  /* Only allowed to report eof if has not yet reported an error */
  DBUG_ASSERT(! is_set());
  /*
    In production, refuse to overwrite an error or a custom response
    with an EOF packet.
  */
  if (is_error() || is_disabled())
    return;

  /*
    If inside a stored procedure, do not return the total
    number of warnings, since they are not available to the client
    anyway.
  */
  m_statement_warn_count= (thd->spcont ?
                           0 : thd->warning_info->statement_warn_count());

  m_status= DA_EOF;
  DBUG_VOID_RETURN;
}

/**
  Set ERROR status.
*/

void
Diagnostics_area::set_error_status(THD *thd, uint sql_errno_arg,
                                   const char *message_arg,
                                   const char *sqlstate)
{
  DBUG_ENTER("set_error_status");
  /*
    Only allowed to report error if has not yet reported a success
    The only exception is when we flush the message to the client,
    an error can happen during the flush.
  */
  DBUG_ASSERT(! is_set() || can_overwrite_status);
#ifdef DBUG_OFF
  /*
    In production, refuse to overwrite a custom response with an
    ERROR packet.
  */
  if (is_disabled())
    return;
#endif

  if (sqlstate == NULL)
    sqlstate= mysql_errno_to_sqlstate(sql_errno_arg);

  m_sql_errno= sql_errno_arg;
  memcpy(m_sqlstate, sqlstate, SQLSTATE_LENGTH);
  m_sqlstate[SQLSTATE_LENGTH]= '\0';
  strmake(m_message, message_arg, sizeof(m_message)-1);

  m_status= DA_ERROR;
  DBUG_VOID_RETURN;
}


/**
  Mark the diagnostics area as 'DISABLED'.

  This is used in rare cases when the COM_ command at hand sends a response
  in a custom format. One example is the query cache, another is
  COM_STMT_PREPARE.
*/

void
Diagnostics_area::disable_status()
{
  DBUG_ASSERT(! is_set());
  m_status= DA_DISABLED;
}

Warning_info::Warning_info(ulonglong warn_id_arg)
  :m_statement_warn_count(0),
  m_current_row_for_warning(1),
  m_warn_id(warn_id_arg),
  m_read_only(FALSE)
{
  /* Initialize sub structures */
  init_sql_alloc(&m_warn_root, WARN_ALLOC_BLOCK_SIZE, WARN_ALLOC_PREALLOC_SIZE);
  m_warn_list.empty();
  bzero((char*) m_warn_count, sizeof(m_warn_count));
}


Warning_info::~Warning_info()
{
  free_root(&m_warn_root,MYF(0));
}


/**
  Reset the warning information of this connection.
*/

void Warning_info::clear_warning_info(ulonglong warn_id_arg)
{
  m_warn_id= warn_id_arg;
  free_root(&m_warn_root, MYF(0));
  bzero((char*) m_warn_count, sizeof(m_warn_count));
  m_warn_list.empty();
  m_statement_warn_count= 0;
  m_current_row_for_warning= 1; /* Start counting from the first row */
}

/**
  Append warnings only if the original contents of the routine
  warning info was replaced.
*/
void Warning_info::merge_with_routine_info(THD *thd, Warning_info *source)
{
  /*
    If a routine body is empty or if a routine did not
    generate any warnings (thus m_warn_id didn't change),
    do not duplicate our own contents by appending the
    contents of the called routine. We know that the called
    routine did not change its warning info.

    On the other hand, if the routine body is not empty and
    some statement in the routine generates a warning or
    uses tables, m_warn_id is guaranteed to have changed.
    In this case we know that the routine warning info
    contains only new warnings, and thus we perform a copy.
  */
  if (m_warn_id != source->m_warn_id)
  {
    /*
      If the invocation of the routine was a standalone statement,
      rather than a sub-statement, in other words, if it's a CALL
      of a procedure, rather than invocation of a function or a
      trigger, we need to clear the current contents of the caller's
      warning info.

      This is per MySQL rules: if a statement generates a warning,
      warnings from the previous statement are flushed.  Normally
      it's done in push_warning(). However, here we don't use
      push_warning() to avoid invocation of condition handlers or
      escalation of warnings to errors.
    */
    opt_clear_warning_info(thd->query_id);
    append_warning_info(thd, source);
  }
}

/**
  Add a warning to the list of warnings. Increment the respective
  counters.
*/
MYSQL_ERROR *Warning_info::push_warning(THD *thd,
                                        uint sql_errno, const char* sqlstate,
                                        MYSQL_ERROR::enum_warning_level level,
                                        const char *msg)
{
  MYSQL_ERROR *cond= NULL;

  if (! m_read_only)
  {
    if (m_warn_list.elements < thd->variables.max_error_count)
    {
      cond= new (& m_warn_root) MYSQL_ERROR(& m_warn_root);
      if (cond)
      {
        cond->set(sql_errno, sqlstate, level, msg);
        m_warn_list.push_back(cond, &m_warn_root);
      }
    }
    m_warn_count[(uint) level]++;
  }

  m_statement_warn_count++;
  return cond;
}

/*
  Push the warning to error list if there is still room in the list

  SYNOPSIS
    push_warning()
    thd			Thread handle
    level		Severity of warning (note, warning)
    code		Error number
    msg			Clear error message
*/

void push_warning(THD *thd, MYSQL_ERROR::enum_warning_level level,
                  uint code, const char *msg)
{
  DBUG_ENTER("push_warning");
  DBUG_PRINT("enter", ("code: %d, msg: %s", code, msg));

  /*
    Calling push_warning/push_warning_printf with a level of
    WARN_LEVEL_ERROR *is* a bug.  Either use my_printf_error(),
    my_error(), or WARN_LEVEL_WARN.
  */
  DBUG_ASSERT(level != MYSQL_ERROR::WARN_LEVEL_ERROR);

  if (level == MYSQL_ERROR::WARN_LEVEL_ERROR)
    level= MYSQL_ERROR::WARN_LEVEL_WARN;

  (void) thd->raise_condition(code, NULL, level, msg);

  DBUG_VOID_RETURN;
}


/*
  Push the warning to error list if there is still room in the list

  SYNOPSIS
    push_warning_printf()
    thd			Thread handle
    level		Severity of warning (note, warning)
    code		Error number
    msg			Clear error message
*/

void push_warning_printf(THD *thd, MYSQL_ERROR::enum_warning_level level,
			 uint code, const char *format, ...)
{
  va_list args;
  char    warning[MYSQL_ERRMSG_SIZE];
  DBUG_ENTER("push_warning_printf");
  DBUG_PRINT("enter",("warning: %u", code));

  DBUG_ASSERT(code != 0);
  DBUG_ASSERT(format != NULL);

  va_start(args,format);
  my_vsnprintf_ex(&my_charset_utf8_general_ci, warning,
                  sizeof(warning), format, args);
  va_end(args);
  push_warning(thd, level, code, warning);
  DBUG_VOID_RETURN;
}


/*
  Send all notes, errors or warnings to the client in a result set

  SYNOPSIS
    mysqld_show_warnings()
    thd			Thread handler
    levels_to_show	Bitmap for which levels to show

  DESCRIPTION
    Takes into account the current LIMIT

  RETURN VALUES
    FALSE ok
    TRUE  Error sending data to client
*/

const LEX_STRING warning_level_names[]=
{
  { C_STRING_WITH_LEN("Note") },
  { C_STRING_WITH_LEN("Warning") },
  { C_STRING_WITH_LEN("Error") },
  { C_STRING_WITH_LEN("?") }
};

bool mysqld_show_warnings(THD *thd, ulong levels_to_show)
{
  List<Item> field_list;
  DBUG_ENTER("mysqld_show_warnings");

  DBUG_ASSERT(thd->warning_info->is_read_only());

  field_list.push_back(new Item_empty_string("Level", 7));
  field_list.push_back(new Item_return_int("Code",4, MYSQL_TYPE_LONG));
  field_list.push_back(new Item_empty_string("Message",MYSQL_ERRMSG_SIZE));

  if (thd->protocol->send_result_set_metadata(&field_list,
                                 Protocol::SEND_NUM_ROWS | Protocol::SEND_EOF))
    DBUG_RETURN(TRUE);

  MYSQL_ERROR *err;
  SELECT_LEX *sel= &thd->lex->select_lex;
  SELECT_LEX_UNIT *unit= &thd->lex->unit;
  ulonglong idx= 0;
  Protocol *protocol=thd->protocol;

  unit->set_limit(sel);

  List_iterator_fast<MYSQL_ERROR> it(thd->warning_info->warn_list());
  while ((err= it++))
  {
    /* Skip levels that the user is not interested in */
    if (!(levels_to_show & ((ulong) 1 << err->get_level())))
      continue;
    if (++idx <= unit->offset_limit_cnt)
      continue;
    if (idx > unit->select_limit_cnt)
      break;
    protocol->prepare_for_resend();
    protocol->store(warning_level_names[err->get_level()].str,
		    warning_level_names[err->get_level()].length,
                    system_charset_info);
    protocol->store((uint32) err->get_sql_errno());
    protocol->store(err->get_message_text(),
                    err->get_message_octet_length(),
                    system_charset_info);
    if (protocol->write())
      DBUG_RETURN(TRUE);
  }
  my_eof(thd);

  thd->warning_info->set_read_only(FALSE);

  DBUG_RETURN(FALSE);
}


/**
   Convert value for dispatch to error message(see WL#751).

   @param to          buffer for converted string
   @param to_length   size of the buffer
   @param from        string which should be converted
   @param from_length string length
   @param from_cs     charset from convert
 
   @retval
   result string
*/

char *err_conv(char *buff, uint to_length, const char *from,
               uint from_length, CHARSET_INFO *from_cs)
{
  char *to= buff;
  const char *from_start= from;
  size_t res;

  DBUG_ASSERT(to_length > 0);
  to_length--;
  if (from_cs == &my_charset_bin)
  {
    uchar char_code;
    res= 0;
    while (1)
    {
      if ((uint)(from - from_start) >= from_length ||
          res >= to_length)
      {
        *to= 0;
        break;
      }

      char_code= ((uchar) *from);
      if (char_code >= 0x20 && char_code <= 0x7E)
      {
        *to++= char_code;
        from++;
        res++;
      }
      else
      {
        if (res + 4 >= to_length)
        {
          *to= 0;
          break;
        }
        res+= my_snprintf(to, 5, "\\x%02X", (uint) char_code);
        to+=4;
        from++;
      }
    }
  }
  else
  {
    uint errors;
    res= copy_and_convert(to, to_length, system_charset_info,
                          from, from_length, from_cs, &errors);
    to[res]= 0;
  }
  return buff;
}


/**
   Convert string for dispatch to client(see WL#751).

   @param to          buffer to convert
   @param to_length   buffer length
   @param to_cs       chraset to convert
   @param from        string from convert
   @param from_length string length
   @param from_cs     charset from convert
   @param errors      count of errors during convertion

   @retval
   length of converted string
*/

uint32 convert_error_message(char *to, uint32 to_length, CHARSET_INFO *to_cs,
                             const char *from, uint32 from_length,
                             CHARSET_INFO *from_cs, uint *errors)
{
  int         cnvres;
  my_wc_t     wc;
  const uchar *from_end= (const uchar*) from+from_length;
  char *to_start= to;
  uchar *to_end= (uchar*) to+to_length;
  my_charset_conv_mb_wc mb_wc= from_cs->cset->mb_wc;
  my_charset_conv_wc_mb wc_mb;
  uint error_count= 0;
  uint length;

  DBUG_ASSERT(to_length > 0);
  to_length--;

  if (!to_cs || from_cs == to_cs || to_cs == &my_charset_bin)
  {
    length= min(to_length, from_length);
    memmove(to, from, length);
    to[length]= 0;
    return length;
  }

  wc_mb= to_cs->cset->wc_mb;
  while (1)
  {
    if ((cnvres= (*mb_wc)(from_cs, &wc, (uchar*) from, from_end)) > 0)
    {
      if (!wc)
        break;
      from+= cnvres;
    }
    else if (cnvres == MY_CS_ILSEQ)
    {
      wc= (ulong) (uchar) *from;
      from+=1;
    }
    else
      break;

    if ((cnvres= (*wc_mb)(to_cs, wc, (uchar*) to, to_end)) > 0)
      to+= cnvres;
    else if (cnvres == MY_CS_ILUNI)
    {
      length= (wc <= 0xFFFF) ? 6/* '\1234' format*/ : 9 /* '\+123456' format*/;
      if ((uchar*)(to + length) >= to_end)
        break;
      cnvres= my_snprintf(to, 9,
                          (wc <= 0xFFFF) ? "\\%04X" : "\\+%06X", (uint) wc);
      to+= cnvres;
    }
    else
      break;
  }

  *to= 0;
  *errors= error_count;
  return (uint32) (to - to_start);
}