Thread: BUG #6645: Getting an error with “ERROR: PL/Perl function must return reference to hash or array”?

The following bug has been logged on the website:

Bug reference:      6645
Logged by:          Evna Carroll
Email address:      me@evancarroll.com
PostgreSQL version: 9.1.2
Operating system:   Linux
Description:

This is a cross post from dba.stackexchange.com:
http://dba.stackexchange.com/q/17998/2639

The follow code used to work in Postgresql 8.4.11 with perl v5.10.1:

=# select * From testfunction();
      testfunction
------------------------
 http://www.google.com/
However, after doing a dump and load into Postgresql 9.1.3 with perl v5.14.2
I get:

ERROR:  PL/Perl function must return reference to hash or array
CONTEXT:  PL/Perl function "testfunction"
For reference, here is the function:

CREATE OR REPLACE FUNCTION testfunction(OUT text) AS $$
  use URI;
  return URI->new('http://www.google.com/')->canonical;
$$ LANGUAGE plperlu;
Again, the version of perl changed from v5.10.1 to v5.14.2; however, the
return from Data::Peek is the same across both versions:

$ perl -MData::Peek -MURI -e'DPeek(
    URI->new(q[http://www.google.com])->canonical
);'
Output on both versions of perl:

\PVMG("http://www.google.com/"\0)

On Wed, May 16, 2012 at 10:47 AM,  <me@evancarroll.com> wrote:
> The following bug has been logged on the website:
>
> Bug reference:      6645
> Logged by:          Evna Carroll
> Email address:      me@evancarroll.com
> PostgreSQL version: 9.1.2
> Operating system:   Linux
> Description:
>
> This is a cross post from dba.stackexchange.com:
> http://dba.stackexchange.com/q/17998/2639
>
> The follow code used to work in Postgresql 8.4.11 with perl v5.10.1:

> CREATE OR REPLACE FUNCTION testfunction(OUT text) AS $$
>  use URI;
>  return URI->new('http://www.google.com/')->canonical;
> $$ LANGUAGE plperlu;

URI->canonical() returns some kind of blessed object, you can get it
to work by coercing the result to a string first:

CREATE OR REPLACE FUNCTION testfunction(OUT text) AS $$
use URI;
return URI->new('http://www.google.com/')->canonical().'';
$$ LANGUAGE plperlu;

We tightened this up over in:

commit 7c64c9f6b767b84597d69cfa2ae03d9a9655ec75
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date:   Thu Oct 13 18:02:43 2011 -0400

    Fix up Perl-to-Postgres datatype conversions in pl/perl.

    This patch restores the pre-9.1 behavior that pl/perl functions returning
    VOID ignore the result value of their last Perl statement.  9.1.0
    unintentionally threw an error if the last statement returned a reference,
    as reported by Amit Khandekar.

    [...snip...]

    In addition, ensure we throw errors for attempts to return arrays or hashes
    when the function's declared result type is not an array or composite type,
    respectively.  Pre-9.1 versions rather uselessly returned strings like
    ARRAY(0x221a9a0) or HASH(0x221aa90), while 9.1.0 threw an error for the
    hash case and returned a garbage value for the array case.

   [...snip...]

As noted above if you return a reference you would get a mostly
useless string like "HASH(0x...)". Post commit above it now gives you
the error "ERROR:  cannot convert Perl hash to non-composite type
text" instead. That seemed better at the time because its almost
always a mistake (with what you return or your declared return type).

That being said it seems we failed to take any magic (aka string
overloads) that a blessed reference might have. Ill see about
submitting a patch for 9.3 (9.2 just entered beta). Anyone have any
thoughts on if we should backpatch a fix?

Alex Hunsaker <badalex@gmail.com> writes:
> That being said it seems we failed to take any magic (aka string
> overloads) that a blessed reference might have. Ill see about
> submitting a patch for 9.3 (9.2 just entered beta). Anyone have any
> thoughts on if we should backpatch a fix?

Right offhand I'd be +1 for making that change, but not for backpatching
it; but I'm not a big plperl user.  Would such a case have worked before
9.1?  If it did and we broke it in 9.1, that would be a good reason to
back-patch into 9.1.  If it never worked, then it sounds like a new
feature.

            regards, tom lane

On Wed, May 16, 2012 at 11:53 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Alex Hunsaker <badalex@gmail.com> writes:
>> That being said it seems we failed to take any magic (aka string
>> overloads) that a blessed reference might have. Ill see about
>> submitting a patch for 9.3 (9.2 just entered beta). Anyone have any
>> thoughts on if we should backpatch a fix?
>
> Right offhand I'd be +1 for making that change, but not for backpatching
> it; but I'm not a big plperl user.  Would such a case have worked before
> 9.1?  If it did and we broke it in 9.1, that would be a good reason to
> back-patch into 9.1.  If it never worked, then it sounds like a new
> feature.

Yeah, it worked pre 9.1.