Support for native sendfile(2) for Perl 6

IO::SendFile.pm6

unit package IO::SendFile;

use NativeCall;

multi sub send-file(IO::Handle:D $input, IO::Handle:D $output, Int:D $count where * > 0) is export {
        given sendfile($output.native-descriptor, $input.native-descriptor, Nil, $count) {
                when -1 {
                        my $errno := cglobal(Str, 'errno', int32);
                        fail strerror($errno);
                }
                default {
                        return $_;
                }
        }
}

multi sub send-file(IO::Handle:D $input, IO::Handle:D $output) is export {
        constant BLOCK-SIZE = 2048;
        my $total = 0;

        loop {
                $total += my $count = send-file($input, $output, BLOCK-SIZE);
                last if $count < BLOCK-SIZE;
        }
}

sub sendfile(int32, int32, Pointer, uint32) returns int32 is native(Str) { * }

sub strerror(int32) returns Str is native(Str) { * }