pub const BAD_EVENT: u16 = 489;Expand description
The status a SUBSCRIBE naming an unserved package is refused with (RFC 6665 §4.2.1.1).
489 and not 400 or 501. It is a specific answer to a specific question — “I do not have that package” — and a subscriber that gets it knows not to retry, where a 400 tells it its request was malformed and a 501 that the method is unimplemented.