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From: Alexander Lakhin <exclusion@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17912: Invalid memory access when converting plpython' array containing empty array
Date: Fri, 28 Apr 2023 21:00:00 +0300
Message-ID: <bf33fe9b-f2f8-5885-aae3-537cd4591386@gmail.com> (raw)
In-Reply-To: <1392974.1682694846@sss.pgh.pa.us>
References: <17912-82ceed78731d9cdc@postgresql.org>
<1392974.1682694846@sss.pgh.pa.us>
Hello Tom,
28.04.2023 18:14, Tom Lane wrote:
> PG Bug reporting form <noreply@postgresql.org> writes:
>> CREATE EXTENSION plpython3u;
>> CREATE OR REPLACE FUNCTION test() RETURNS text[] AS $$
>> return [[], "a"]
>> $$ LANGUAGE plpython3u;
>> SELECT test();
>> As I can see, for the first case we get len = 0 in PLySequence_ToArray();
>> elems, nulls palloc'ed with zero elements, but PLyObject_ToScalar() tries
>> to write a value into nulls[0]...
> Yeah. The calculation of the array size is being done in the wrong
> place, so that we may update len to zero before breaking out of the
> loop. But really it's poor coding for this function to be doing
> its own calculation of the array size at all, rather than consulting
> the authoritative ArrayGetNItems(). I think we need something like
> the attached.
Thank you! I've read the message of the commit you just pushed,
and I confirm that there are another oddities in that area. For example:
CREATE OR REPLACE FUNCTION test() RETURNS text[] AS $$
return [1, [2]]
$$ LANGUAGE plpython3u;
SELECT test();
---------
{1,[2]}
But:
CREATE OR REPLACE FUNCTION test() RETURNS text[] AS $$
return [[1], 2]
$$ LANGUAGE plpython3u;
SELECT test();
ERROR: wrong length of inner sequence: has length -1, but 1 was expected
DETAIL: To construct a multidimensional array, the inner sequences must all have the same length.
CONTEXT: while creating return value
PL/Python function "test"
Or:
CREATE OR REPLACE FUNCTION test() RETURNS text[] AS $$
return [["1"], "abc"]
$$ LANGUAGE plpython3u;
SELECT test();
ERROR: wrong length of inner sequence: has length 3, but 1 was expected
DETAIL: To construct a multidimensional array, the inner sequences must all have the same length.
CONTEXT: while creating return value
PL/Python function "test"
Though may be it's okay, considering python's concepts of
strings/arrays/sequences, or at least deserves a separate discussion.
Best regards,
Alexander
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