Re: Query execution in Perl TAP tests needs work

On 2023-08-30 We 21:29, Thomas Munro wrote:
> On Thu, Aug 31, 2023 at 10:32 AM Andrew Dunstan<andrew@dunslane.net>  wrote:
>> #!/usr/bin/perl
>>
>> use strict; use warnings;
>>
>> use FFI::Platypus;
>>
>> my $ffi = FFI::Platypus->new(api=>1);
>> $ffi->lib("inst/lib/libpq.so");
>>
>>
>> $ffi->type('opaque' => 'PGconn');
>> $ffi->attach(PQconnectdb => [ 'string' ] => 'PGconn');
>> $ffi->attach(PQfinish => [ 'PGconn' ] => 'void');
>>
>> $ffi->type('opaque' => 'PGresult');
>> $ffi->attach(PQexec => [ 'PGconn', 'string' ] => 'PGresult');
>> $ffi->attach(PQgetvalue => [ 'PGresult', 'int', 'int' ] => 'string');
>>
>> my $pgconn = PQconnectdb("dbname=postgres host=/tmp");
>> my $res = PQexec($pgconn, "select count(*) from pg_class");
>> my $count = PQgetvalue( $res, 0, 0);
>>
>> print "count: $count\n";
>>
>> PQfinish($pgconn);
> It looks very promising so far.  How hard would it be for us to add
> this dependency?  Mostly pinging build farm owners?
>
> I'm still on the fence, but the more I know about IPC::Run, the better
> the various let's-connect-directly-from-Perl options sound...


Here's some progress. I have put it all in a perl module, which I have 
tested on Windows (both mingw and MSVC) as well as Ubuntu. I think this 
is probably something worth having in itself. I wrapped a substantial 
portion of libpq, but left out things to do with large objects, async 
processing, pipelining, SSL and some other things. We can fill in the 
gaps in due course.

The test program now looks like this:

    use strict;
    use warnings;

    use lib ".";
    use PqFFI;

    PqFFI::setup("inst/lib");

    my $conn = PQconnectdb("dbname=postgres host=/tmp");
    my $res = PQexec($conn, 'select count(*) from pg_class');
    my $count = PQgetvalue($res,0,0);
    print "$count rows in pg_class\n";
    PQfinish($conn);

I guess the next thing would be to test it on a few more platforms and 
also to see if we need to expand the coverage of libpq for the intended 
uses.

I confess I'm a little reluctant to impose this burden on buildfarm 
owners. We should think about some sort of fallback in case this isn't 
supported on some platform, either due to technological barriers or 
buildfarm owner reluctance.


cheers


andrew


--
Andrew Dunstan
EDB:https://www.enterprisedb.com