FreeTDS Development Group

["Mark Gruetzner" <mgruetzner AT rw3.com>]

Thanks,

Yes, my first instinct, as well, was to widen the message variable to 32
bits to store the message number.  Not being very familiar with the code and
the specs, I was more afraid of breaking something by doing that....but, I
agree, this would be getting to the real root of the problem...

As for the "2 sets of database results" (which I now know is only 1 set +
out of band data for the message), I was simply looking at the freetds.log
file (which works very well for debugging by the way) and found that I was
receiving both my query results and the message from raiserror in response
to my call to mssql_query--but the php code was only getting the query
results with the first call to dbresults() and the message was not getting
processed.  In this case, where there is out-of-band data following the
query results, the first call to dbresults() returns SUCCESS (rather than
NO_MORE_RESULTS), and so I call it again (after processing all the rows with
dbnextrow) which will then return NO_MORE_RESULTS and cause the message to
get processed--which in turn causes the PHP callback to get called by
freetds, where PHP stores the message for subsequent calls to
mssql_get_last_message.  (By the way, PHP calls dbmsghandle to register its
callback function which freetds calls when it processes a message--then, in
the callback function, PHP simply stores the message in a global variable so
it can return it when the PHP function msssql_get_last_message() is called)

I'd be interested in looking at an actual spec. since I have been solely
relying on looking at the source code and the freetds.log file...

-Mark


-----Original Message-----
From: bounce-freetds-143882 AT franklin.oit.unc.edu
[mailto:bounce-freetds-143882 AT franklin.oit.unc.edu]On Behalf Of Lowden,
James K
Sent: Friday, May 17, 2002 2:42 PM
To: TDS Development Group
Subject: [freetds] RE: mssql_query not updating mssql_get_last_message
on php4.1.2 and freetds 0.53


> From: Mark Gruetzner [mailto:mgruetzner AT rw3.com]
> Sent: May 17, 2002 12:11 PM

Mark,

Nice analysis.  Always good to improve the fit of FreeTDS and PHP.  I don't
think it's a question of "negative message numbers" per se, see below, but
maybe I'm overlooking something.

> mssql_query ("mystoredproc");
> $msg = mssql_get_last_message ();
> print $msg;
>
> where "mystoredproc" is a stored procedure that returns N rows of data and
> calls the SQL function below to send a warning message:
>
> raiserror ('QueryLimit',9,1)
>
> you would expect the value of $msg to be "QueryLimit" after the call to
> mssql_query.  In fact, this is how it works on Windows but not on Linux
> using freetds.  I have debugged this issue on both the freetds and php
> software and found the following.  On Freetds, the message number that
gets
> returned from SQL is 50000 which when stored as a 16-bit signed integer is
a
> negative value in the freetds code, so the freetds code ignores the
message.

raiserror is so weird.  It passes a string and a message number, and can
optionally set @@error to value of the message id ("with seterror").

To get raiserror to pass a user-defined message number, you need to install
the message in sysmessages with sp_addmessage.  The syntax you're using is
an "ad hoc message", to which raiserror assigns a message number of 50,000.
That's where the 50,000 is coming from.

The maximum message number is 2^31 - 1.  We need 31 bits to represent such
numbers, not the 15 we're apparently providing.  Trying to stuff 31 bits of
data into a signed two-byte variable is unlikely to be a Good Thing.  In
this case, the 50,000 only *coincidentally* needs just 16 bits, so you see
it as a negative value (high bit set).  But someone could add, say, message
number 131,196 (2^17 + 124) to sysmessages; we'd trim off the high bytes and
represent it as #124, "CREATE PROCEDURE contains no statements".  A bug, I'd
say.

The real error is treating the message id as a 16-bit variable, no?  Where
does that happen?  Why not just widen the variable?

What this means for Sybase, TDS 4.2, and/or big endian machines, I don't
know.

> I modified the freetds code to NOT ignore negative message numbers but to
go
> ahead and pass those messages on to the appropriate callback function in
> PHP.  That helped matters, but there was still an issue in the php code in
> the "sybase_query" function in php_sybase_db.c.  Basically, what is
> happening is that in the case described above, you receive 2 sets of
> database results as a result of the query, but the sybase_query function
is
> only reading the first set of results.

How does it become "2 sets of database results"?  There is a result set
(output from your query), and an out-of-band message (from raiserror).
Those are two different things.

mssql_get_last_message doesn't process result sets; it looks to me like the
PHP equivilant of dbmsghandle.

Obviously, I don't know all the ramifications, either, Mark.  I'm just
trying to make sure we understand the spec first.

Regards,
--jkl

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