Re: SystemError: null argument to internal routine

On Thu, Mar 3, 2011 at 8:02 PM, Jan Urbański <wulczer@wulczer.org> wrote:
> On 03/03/11 20:52, Eric Snow wrote:
>> I am trying to figure out the conditions under which I get that
>> SystemError.  Here is a simple way that I found to reproduce the
>> problem:
>>
>>>>> import psycopg2
>>>>> psycopg2.__version__
>> '2.3.2 (dt dec pq3 ext)'
>>>>> conn = psycopg2.connect("...")
>>>>> cur = conn.cursor()
>>>>> cur.execute(";")
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in ?
>> SystemError: null argument to internal routine
>>
>> I am getting the same exception during a call to copy_expert.  How would
>> the data I pass in there trigger the same exception as when I pass a
>> single semicolon?  I am guessing that it does not even make it over the
>> wire to the postgres server when the exception is raised.  Thanks.
>
> Aaah, that rings a bell. I was getting the same error with txpostgres
> and even once found out why, but forgot, and now I remembered.
>
> I believe that the problem is in pqpath.c, in pq_fetch. There's a switch
> statement there that checks the result of PQresultStatus and does not
> take PGRES_EMPTY_QUERY into consideration.
>
> The code that jumps to the default: label, which leads it to pq_raise.
> Towards the end there's a
>
> if (code != NULL)
>   exc = exception_from_sqlstate(code);
>
> which AFAIR never gets executed, because code *is* NULL. And then it
> hits psyco_set_error with a NULL exception, this leads to the "NULL
> argument to internal routine" error.
>
> I might have messed up some details, but I'm pretty sure the problem is
> not handling PGRES_EMPTY_QUERY correctly.

Thank you for the report: open ticket #46
<http://psycopg.lighthouseapp.com/projects/62710-psycopg/tickets/46>

If anyone wants to try to solve it, please add a comment to the
tracker. Otherwise I will take a look at it as soon as I have a
moment.

-- Daniele