use utf8;
use feature ':5.10';

use Encode qw/:fallback_all/;
use PerlIO::encoding;
BEGIN{ $PerlIO::encoding::fallback = FB_WARN; }
use open IO => ':encoding(UTF-8)', ':std';

# show current PerIO layers of stdout on stderr
my @layers = PerlIO::get_layers(STDOUT, details => 1);
for (my $i=0; $i<@layers; $i+=3) {
    printf STDERR "stdout layer %d: (%s,%s,0x%X)\n", $i/3,
	$layers[$i], $layers[$i+1]||'',$layers[$i+2];
}
print STDERR "\n";

# show [a] that Encode works, and [b] the bytes around the bad area.
sub examine($) {
    my $s = shift;

    my $encoded = Encode::encode( "UTF-8", $s, FB_CROAK );
    warn "# utf-8 encoded octet dump (total=", length($encoded), "):\n";



    my @x = unpack("C*", $encoded);
    for ( my $i=1010; $i<1028; ++$i ) {
	printf STDERR " enc[%d]=0x%02X", $i, $x[$i];
    }
    print STDERR "\n";
}

# create sample test string
my $test = '';
while ( length($test) <= 520 ) { # typically 2-byte codes
    $test .= ' &#1087;&#1088;&#1077;&#1076;&#1086;&#1089;&#1090;&#1072;&#1074;&#1083;&#1077;&#1085;&#1072;';
}
print "encoded: " . (utf8::is_utf8($test) ? 'yes' : 'no') . "\n";
my $len = length $test;
print "length: $len\n";

# this one works
examine($test);
print "$test\n\n";

# add a 1-byte UTF-8 code point (x) in front, and it fails
# in the presence of "use PerlIO::encoding" or "use open IO => .."
$test = 'x' . $test;

print "encoded: " . (utf8::is_utf8($test) ? 'yes' : 'no') . "\n";
$len = length $test;

print "length: $len\n";

examine($test);
print "$test\n\n";