Problem:
func is_alphanumeric is a part of func is_token_char, but the two functions are all called by is_request_uri_char.
fn is_token_char(b: u8) → bool {
is_alphanumeric(b) || b"!%'*±._`~".contains(&b)
}
fn is_request_uri_char(b: u8) → bool {
is_alphanumeric(b) || is_token_char(b) || b"~#@:;=?+&$,/".contains(&b)
}