sub write {
    @_ == 3 or croak 'Usage: $sftp->write($fh, $data)';

    my ($sftp, $rfh) = @_;
    $sftp->flush($rfh, 'in') or return undef;

    if (utf8::is_utf8($_[2])) {
        splice(@_, 2, 1, "$_[2]");   # Don't affect caller.
        utf8::downgrade($_[2], 1)  # Change format to bytes.
            or carp("Can only write bytes to a socket");
    }
    ...