fn is_ws(b: u8) -> bool {
    b == b' ' || b == b'\t' || b == b'\n' || b == b'\r' || b == 11u8 || b == 12u8
}
pub fn header_field_ok(s: &[u8]) -> bool {
    let mut ok = true;
    let mut i = 0usize;
    while i < s.len() {
        if s[i] >= 128 || is_ws(s[i]) {
            ok = false;
        }
        i += 1;
    }
    ok
}