use IPC::Open3;
use POSIX ":sys_wait_h";

package Query;  
sub new {
    my $self = shift;
    my %opt = @_;
    $self = \%opt;
    defined $self -> { SERVICE }
        or $self -> { SERVICE } = 'defaultqueryprog';
    if ( defined $self -> { SEND } ) {
        my $pid = open3 my $wh, my $rh, my $eh,
            $self -> { SERVICE }
            or warn "$!: " . $self -> { SERVICE } . "\n"
            && exit $?;
        $self -> { WH } = $wh;
        $self -> { RH } = $rh;
        $self -> { EH } = $eh;
        $self -> { PID } = $pid;
        write $wh $self -> { SEND } . "\n";
    }
    else {
        my $pid = open3 undef(), my $rh, my $eh,
            $self -> { SERVICE }
            or warn "$!: " . $self -> { SERVICE } . "\n"
            && exit $?;
        $self -> { RH } = $rh;
        $self -> { EH } = $eh;
        $self -> { PID } = $pid;
    }
    return bless $self; # note the pipe is not closed!
}
sub fetch {
    my $self = shift;
    my $rh = $self -> { RH };
    my $eh = $self -> { EH };
    my $oneliner = !wantarray;
    unless ( $oneliner &&= <$rh> ) {
        # cleanup if and only if flushing the pipe
        my @out = <$rh>;
        close $rh;
        my @err = <$eh>;
        close $eh;
        $self -> { STDERR } = \@err;
        waitpid $self -> { PID },0;
        delete $self -> { PID };
        return @out;
    }
    return $oneliner;
}

sub fetcherror { # similar to fetch but on $self -> { EH };
...
}
sub shut {
    my $self = shift;
    close $self -> { RH }, $self -> { EH };
    $sts = $?;
    waitpid $self -> { PID }, 0;
    delete $self -> { PID };
    return $sts;
}
1;