[freetds] 0.64 crashes in PHP with NULL value TEXT type

Lowden, James K james.k.lowden at alliancebernstein.com
Fri Jul 28 14:19:25 EDT 2006


> From: L J Bayuk
> Sent: Thursday, July 27, 2006 9:06 PM
> 
> I've been happily using FreeTDS-0.63 talking to Sybase SQL Anywhere
> (ASA), mostly with PHP and the sybase_ct module, and occasionally
> with sqsh.
> 
> I built and tested FreeTDS-0.64 and it crashes PHP in one of my
> tests.  The specific case is a TEXT type field (this is an unlimited
> length VARCHAR) with value NULL. When I select a record with a NULL
> text field, PHP crashes something like this:
>   #1  0x080f473b in _estrndup (s=0x81e125c "", length=136306688)
>      at .../php-4.4.2/Zend/zend_alloc.c:387
>   #2  0x40227ab7 in php_sybase_fetch_result_row (result=0x81ab678,
>   numrows=-1)
>      at .../sybase_ct/php_sybase_ct.c:1185
>   #3  0x40228346 in php_sybase_fetch_result_set (sybase_ptr=0x81b983c,
>      buffered=0, store=-1)
>      at .../sybase_ct/php_sybase_ct.c:1333
> Note that it is crashing in the PHP module, not FreeTDS/ctlib. But
> it isn't PHP's fault. See the length= parameter above. PHP is trying
> to store the result for the TEXT field. It should have gotten the
> message that the field is NULL, but it didn't, and ended up trying
> to copy an absurd amount of data. It works OK for CHAR and VARCHAR,
> but not for TEXT fields.
> 
> Speculation:  Using the TDSDUMP log, I see that in ctbind(),
> column_cur_size is set to 0, not -1 (which would set the indicator
> to -1 indicating NULL) for this TEXT type. But I think the cause
> is earlier.
> 
> Here's a bit of the TDSDUMP log. The query gets 1 record with 4
> fields: an INTEGER, a CHAR which is an empty string, a VARCHAR
> which is NULL, and a TEXT which is NULL.
> 
> token.c:526:processing result tokens.  marker is  d1(ROW)
> token.c:1863:tds_get_data: column 0, type 56, varint size 0
> token.c:1920:processing row.  column size is 4
token.c:1863:tds_get_data:
> column 1, type 39, varint size 1 token.c:1920:processing row.
> column size is 1 token.c:1863:tds_get_data: column 2, type 39,
> varint size 1 token.c:1920:processing row.  column size is -1
> token.c:1863:tds_get_data: column 3, type 35, varint size 4
> token.c:1920:processing row.  column size is 0
> 
> I think 'column size is 0' should be -1 in the last case, as that
> is the NULL indicator. But I'm over my head here. Help, please?

Thank you for the report.  I don't know what's wrong, but I don't think
that's it.  

I tried two queries in sqsh.  A zero-length text field reports a length
of 0; a NULL text field of -1.  

$ TDSDUMP=stdout sqsh  -C"set textsize 30 select cast('' as text) as
nothing" \
	| sed -ne'/^ *nothing/,/ct_results/p'
 nothing
 ------------------------------
ct.c:1454:ct_fetch()
util.c:119:Changing query state from PENDING to READING
token.c:526:processing result tokens.  marker is  d1(ROW)
token.c:1863:tds_get_data: column 0, type 35, varint size 4
token.c:1920:processing row.  column size is 0
                                            ^^^
util.c:119:Changing query state from READING to PENDING
ct.c:1519:inside ct_fetch()process_row_tokens returned 1
ct.c:1670:_ct_bind_data()
ct.c:1677:_ct_bind_data(): column_type: 35 column_len: 0
ct.c:1971:_ct_get_server_type(0)
ct.c:1858:_ct_get_client_type(type 35, user 0, size 30)
cs.c:351:cs_convert()
ct.c:1971:_ct_get_server_type(4)
ct.c:1971:_ct_get_server_type(0)
cs.c:358:cs_convert() srctype = 35 (0) desttype = 47 (31)
cs.c:371:cs_convert() srcdata is null

ct.c:1454:ct_fetch()
ct.c:1064:ct_results()

$ TDSDUMP=stdout sqsh  -C"set textsize 30 select cast(NULL as text) as
nothing" \
	| sed -ne'/^ *nothing/,/ct_results/p'
 nothing
 ------------------------------
ct.c:1454:ct_fetch()
util.c:119:Changing query state from PENDING to READING
token.c:526:processing result tokens.  marker is  d1(ROW)
token.c:1863:tds_get_data: column 0, type 35, varint size 4
token.c:1920:processing row.  column size is -1
                                             ^^^
util.c:119:Changing query state from READING to PENDING
ct.c:1519:inside ct_fetch()process_row_tokens returned 1
ct.c:1670:_ct_bind_data()
ct.c:1677:_ct_bind_data(): column_type: 35 column_len: -1
ct.c:1971:_ct_get_server_type(0)
 NULL
ct.c:1454:ct_fetch()
ct.c:1064:ct_results()

sqsh binds both correctly.  Do you see similar ct_bind_data messages
using PHP?  

I am using TDS 7.0, however, not 5.0 as with ASA.  Perhaps you could try
my queries on your server and let me know?  

Regards, 

--jkl

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