Re: BUG #5748: Invalid oidvector data during binary recv

On 2010-11-15 11:40, Heikki Linnakangas wrote:
> On 15.11.2010 12:08, Yeb Havinga wrote:
>> On 2010-11-11 17:02, Heikki Linnakangas wrote:
>>> On 11.11.2010 17:48, Tom Lane wrote:
>>>> "Yeb Havinga"<yebhavinga@gmail.com> writes:
>>>>> postgres=# create table a as select ''::oidvector;
>>>>> SELECT 1
>>>>> postgres=# copy a to '/tmp/test' with binary;
>>>>> COPY 1
>>>>> postgres=# copy a from '/tmp/test' with binary;
>>>>> ERROR: invalid oidvector data
>>>>
>>>> The problem seems to be that array_recv passes back a zero-dimensional
>>>> array, *not* a 1-D array, when it observes that the input has no
>>>> elements. A zero-D array is not part of the subset of possible arrays
>>>> that we allow for oidvector.
>>>
>>> Yeah, I just reached that conclusion too..
>> The patch below changes array_recv, so that it returns an empty 1-D
>> array when an empty 1-D array was written binary. No changes in
>> oidvectorrecv or int2vectorrecv are needed.
>
> That seems like a bad idea. array_in() represents an empty array with
> zero dimensions, we're not going to change the generic array_recv()
> function used for all arrays to behave differently because of some
> corner-case in oidvectorrecv.
It's possible to trigger it with any element type, as long as the use
manages to construct a 1-D array. E.g. with contrib/_int.sql loaded,
array substraction is possible. Now:
postgres=# select ARRAY[1]::int4[] - ARRAY[1]::int4[];
  ?column?
----------
  {}
(1 row)

postgres=# select array_ndims(ARRAY[1]::int4[] - ARRAY[1]::int4[]);
  array_ndims
-------------
            1
(1 row)

Binary send and recv of the value at hand would change it into a 0-D vector.

>
> If we want do anything about this, the right fix is to add a special
> case in oidvectorrecv/int2vectorrecv to handle empty array.
Judging from the fact that it also happens with int4 arrays, this seems
like the wrong place.

regards,
Yeb Havinga