Re: unknownin/out patch (was [HACKERS] PQescapeBytea is

Joe Conway wrote:
> Tatsuo Ishii wrote:
>  >>> Tatsuo Ishii wrote:
>  >>>
>  >>>>
>  >>>> Try a multibyte encoding database. For example,
>  >>>>
>  >>>> $ createdb -E EUC_JP test $ psql -c 'SELECT
>  >>>> SUBSTRING('1234567890' FROM 3)' test substring ----------- 3456
>  >>>>
> 
>  >>>> (1 row)
>  >>>>
>  >>>> Apparently this is wrong. -- Tatsuo Ishii
>  >>>
>  >>> This problem exists in CVS tip *without* the unknownin/out
>  >>> patch:
>  >>
>  >> Sure. That has been broken for a while.
>  >
>  >
>  > I guess this actually happened in 1.79 of varlena.c:
>  >
> Yes, I was just looking at that also. It doesn't consider the case of n 
> = -1 for MB. See the lines:
> 
> #ifdef MULTIBYTE
>    eml = pg_database_encoding_max_length ();
> 
>    if (eml > 1)
>    {
>       sm = 0;
>       sn = (m + n) * eml + 3;
>    }
> #endif
> 
> When n = -1 this does the wrong thing. And also a few lines later:
> 
> #ifdef MULTIBYTE
>    len = pg_mbstrlen_with_len (VARDATA (string), sn - 3);
> 
> I think both places need to test for n = -1. Do you agree?
> 
> 
> Joe
> 

The attached patch should fix the bug reported by Tatsuo.

# psql -U postgres testjp
Welcome to psql, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
        \h for help with SQL commands
        \? for help on internal slash commands
        \g or terminate with semicolon to execute query
        \q to quit

testjp=# SELECT SUBSTRING('1234567890' FROM 3);
  substring
------------
  34567890
(1 row)

Joe
*** pgsql/src/backend/utils/adt/varlena.c	Sun Apr  7 11:44:54 2002
--- pgsql.orig/src/backend/utils/adt/varlena.c	Mon Apr  8 22:32:16 2002
***************
*** 413,419 ****
  	if (eml > 1)
  	{
  		sm = 0;
! 		sn = (m + n) * eml + 3; /* +3 to avoid mb characters overhanging slice end */
  	}
  #endif 
  
--- 373,382 ----
  	if (eml > 1)
  	{
  		sm = 0;
! 		if (n > -1)
! 			sn = (m + n) * eml + 3; /* +3 to avoid mb characters overhanging slice end */
! 		else
! 			sn = n;		/* n < 0 is special-cased by heap_tuple_untoast_attr_slice */
  	}
  #endif 
  
***************
*** 427,433 ****
  	PG_RETURN_NULL();   /* notreached: suppress compiler warning */
  #endif
  #ifdef MULTIBYTE
! 	len = pg_mbstrlen_with_len (VARDATA (string), sn - 3);
  
  	if (m > len)
  	{
--- 390,399 ----
  	PG_RETURN_NULL();   /* notreached: suppress compiler warning */
  #endif
  #ifdef MULTIBYTE
! 	if (n > -1)
! 		len = pg_mbstrlen_with_len (VARDATA (string), sn - 3);
! 	else	/* n < 0 is special-cased; need full string length */
! 		len = pg_mbstrlen (VARDATA (string));
  
  	if (m > len)
  	{