floss: enforce truncate string to be at char boundary

}

impl UInputDev {

    fn floor_char_boundary(str: &String, upper_bound: usize) -> usize {

        // Some string operation can only be done at UTF8 boundary, e.g. truncate.

        // It is guaranteed that there would be at least one such boundary in every 4 bytes,

        // therefore we can just brute force it.

        // This can be replaced with str::floor_char_boundary() once that function is available.

        if str.len() < upper_bound {

            return str.len();

        }

        for i in (0..upper_bound + 1).rev() {

            if str.is_char_boundary(i) {

                return i;

            }

        }

        return 0;

    }

    #[allow(temporary_cstring_as_ptr)]

    fn init(&mut self, mut name: String, addr: String) -> Result<(), String> {

        // Truncate the device name if over the max size allowed.

        name.truncate(UINPUT_MAX_NAME_SIZE - UINPUT_SUFFIX_SIZE);

        let new_len = Self::floor_char_boundary(&name, UINPUT_MAX_NAME_SIZE - UINPUT_SUFFIX_SIZE);

        name.truncate(new_len);

        name.push_str(UINPUT_SUFFIX);

        for (i, ch) in name.chars().enumerate() {

            self.device.name[i] = ch as libc::c_char;