my $in_text = '...';
my $out_text;

open(my $in_fh, '<', \$in_text)
   or die("Unable to create input file handle from string: $!\n");

open(my $out_fh, '>', \$out_text)
   or die("Unable to create output file handle from string: $!\n");

my $decoded = $decoder->decode($in_fh, $out_fh);