[freetds] dbbind, dbnullbind issues

Lowden, James K LowdenJK at bernstein.com
Wed Jun 16 11:05:07 EDT 2004


> From: freetds-bounces at lists.ibiblio.org
> [mailto:freetds-bounces at lists.ibiblio.org]On Behalf Of 
> Thompson, Bill D
> 
> > I loaded your results into a database ...
> 
> Do you ever find youself incapable of thinking about anything 
> except in relational terms :-) ?

Other way?  There's another way?  

> NTBSTRINGBIND right trims any spaces from the character 
> string. Both add a NULL terminator to the data.
> 
> You are supposed to have enough bound space to hold the data 
> and the null terminator.

Right, exactly.  

> My version of NTBSTRINGBIND and STRINGBIND report truncation 
> because there
> isn't enough space for the data + the null term.
> 
> NTBSTRINGBIND only checks for truncation AFTER the removal of 
> the trailing blanks. 
> Otherwise it might report POTENTIAL truncation when in fact 
> no truncation has really occurred.
> 
> Does this look good to you ?

Yes.  That makes it consistent with the varlen=5 case.  We'll just have to document somewhere that FreeTDS's implementation is not subject to the caveat expressed in Sybase's note.  

There's bound to be (pardon the pun) some application out there treating "ind != 0" as NULL or "ind != -1" as OK, and getting away with it because of the idiosyncrasies of the library they're using.  But they're both incorrectly coded and mistreating their data.  We can help.  ;-)

Apart from the fact that I find myself wishing none of this was necessary -- how many ways to bind a string? -- I am glad you've endeavored to get it right at last.  Silently slicing off characters from strings is the sort of bug that's very hard to find in an application; probably someone's suffering from it right now without knowing.  On his behalf, especially because he could be me: Thanks.  

--jkl


> > -----Original Message-----
> > From:	James K. Lowden [SMTP:jklowden at schemamania.org]
> > Sent:	16 June 2004 07:01
> > To:	FreeTDS Development Group
> > Subject:	Re: [freetds] dbbind, dbnullbind issues
> > 
> > On Tue, 15 Jun 2004, "Thompson, Bill D (London)" 
> <bill_d_thompson at ml.com>
> > wrote:
> > 
> > > I think I've reached a kind of understanding of what is 
> happening, by
> > > some extensive testing.
> > 
> > Thanks for doing this, Bill.  Very thorough work.  
> > 
> > > I've got a table with a single row and a single column  - 
> char(10) -
> > > with data '1234567890' in it...
> > 
> > I mean, really, you've been working too hard or something.  
> That's the
> > most boring data imaginable.  
> > 
> > I loaded your results into a database and found this:
> > 
> > [25] varley.FreeTDS.1> select count(*), bindlen, ind from 
> bind_results
> > group by bindlen, ind order by bindlen, ind
> > [25] varley.FreeTDS.2> go
> >              bindlen ind   
> >  ----------- ------- ------
> >            2      -1      0
> >            2      -1     10
> >            3       0      0
> >            1       0     10
> >            4       5     10
> >            4      10      0
> >            4      11      0
> >            4      12      0
> > 
> > (8 rows affected)
> > 
> > By the book, bindlen (varlen) of -1 should never work.  If 
> we don't reject
> > it outright, we should treat it as 0, never mind what 
> Sybase does.  I
> > note, ahem, that bsqldb uses -1.  So much for setting a 
> good example.  
> > 
> > varlen of 0 appears broken in the case of STRINGBIND:
> > 
> > [27] varley.FreeTDS.1> select * from bind_results where 
> bindlen = 0 order
> > by len, ind, type
> > [27] varley.FreeTDS.2> go
> >  type                 bindlen data                      len 
>    ind   
> >  -------------------- ------- ------------------------- 
> ------ ------
> >  CHARBIND                   0 >1234567890@@@@@@@@@@<      
> NULL      0
> >  NTBSTRINGBIND              0 >1234567890<                
> NULL      0
> >  STRINGBIND                 0 >1234567890<                
> NULL     10
> >  VARYCHARBIND               0 >1234567890@@@@@@@@@@<        
> 10      0
> > 
> > The dbnullbind() indicator should be >0 only to indicate 
> truncation. 
> > Because a varlen of 0 passes no information about the buffer's size,
> > db-lib can't possibly know where to truncate the data, nor does it
> > truncate them.  
> > 
> > IMO this is a case for "do it right and let 'em complain".  Any
> > application relying on STRINGBIND's broken behavior is 
> itself broken.  
> > 
> > varlen of 5 seems fine.  It puts lie to the dbnullbind() 
> note "Detection
> > of character string truncation is implemented only for CHARBIND and
> > VARYCHARBIND."  
> > 
> > varlen of 10 is interesting:  
> > 
> > [28] varley.FreeTDS.1> select * from bind_results where 
> bindlen = 10 order
> > by len, ind, type
> > [28] varley.FreeTDS.2> go
> >  type                 bindlen data                      len 
>    ind   
> >  -------------------- ------- ------------------------- 
> ------ ------
> >  CHARBIND                  10 >1234567890@@@@@@@@@@<      
> NULL      0
> >  NTBSTRINGBIND             10 >123456789<                 
> NULL      0
> >  STRINGBIND                10 >123456789<                 
> NULL      0
> >  VARYCHARBIND              10 >1234567890@@@@@@@@@@<        
> 10      0
> > 
> > CHARBIND and VARYCHARBIND *could* report truncation, but in 
> this case no
> > truncation occurs and is thus not reported.  
> > 
> > > In the light of this, I'm not going to populate the 
> indicator variables
> > > at all for NTBSTRINGBIND and STRINGBIND, as there seems 
> to be no logic
> > > to the observable behaviour.
> > 
> > NTBSTRINGBIND and STRINGBIND should but don't report 
> truncation (but the
> > note says that's not "implemented").  Here again, ISTM we 
> can and should
> > report the truncation.  There's no need to replicate 
> Sybase's off-by-one
> > error.  We'll only be making this case consistent with the 
> varlen 5 case. 
> > 
> > 
> > (I suppose one could argue the documentation is right even 
> without the
> > note.  Truncation is reported if the binding "did not 
> specify any data
> > conversions".  If tacking a NULL onto the data is "conversion", then
> > truncation won't be reported....  But you won't hear *me* 
> making that
> > case.)  
> > 
> > Two questions for you, if I may:
> > 
> > 1.  Does dbnullbind() at least report NULLs correctly?  
> > 2.  Does dbanullbind() show similar inconsistencies?  
> > 
> > Regards, 
> > 
> > --jkl
> > 
> > 
> > > > -----Original Message-----
> > > > From:	Lowden, James K [SMTP:LowdenJK at bernstein.com]
> > > > Sent:	15 June 2004 15:13
> > > > To:	FreeTDS Development Group
> > > > Subject:	RE: [freetds] dbbind, dbnullbind issues
> > > > 
> > > > > From: freetds-bounces at lists.ibiblio.org
> > > > > [mailto:freetds-bounces at lists.ibiblio.org]On Behalf Of 
> > > > > Thompson, Bill D
> > > > > 
> > > > > I've been wrestling with the features of dbbind and 
> > > > > dbnullbind
> > > > ...
> > > > > I could do several things:
> > > > > 
> > > > > 1) code our dblibrary funstions so that they behave as 
> > > > > specified in the manual pages.
> > > > > 2) attempt to reflect the actual (but inconsistent) behaviour 
> > > > > of the Sybase implementation
> > > > > 3) code to a different, but clearer and arguably more 
> sensible,
> > > > > specification.
> > > > 
> > > > Hi Bill, 
> > > > 
> > > > Can you cite an example where someone following the 
> letter of the
> > > > documentation would build a non-working application 
> when linking to
> > > > one of the vendors' libraries?  
> > > > 
> > > > In general, I'm sure you agree that adhering to the 
> documents is best.
> > > > Bug-for-bug compatibility is useful in two cases:
> > > > 
> > > > 1.  Following the docs doesn't actually work.  
> > > > 2.  Binary compatibility.  
> > > > 
> > > > The first case is truly bad, and I don't know of any 
> examples.  The
> > > > second is a far-off goal; we'll cross that bridge when 
> we come to it,
> > > > IMO.  
> > > > 
> > > > The other kind of not-of-the-docs behavior are things 
> that work but
> > > > aren't documented to work, things like using varlen of 
> -1 that you
> > > > found.  I think it's fine to support them when it's 
> convenient, and
> > > > deny them when not.  Anyone who complains can fix his 
> code or change
> > > > ours.  
> > > > 
> > > > Is that any help?  
> > > > 
> > > > --jkl

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