pub fn granted_expiry(requested: Duration, policy_maximum: Duration) -> DurationExpand description
The expiry a notifier grants for a requested one (RFC 6665 §4.2.1.1).
“The server MAY shorten the interval but MUST NOT lengthen it” — the same rule REGISTER has, and for the same reason: the shorter of the two is what both sides can agree on without one of them believing in a subscription the other has forgotten.
A request for zero is an unsubscribe (§3.1.1) and stays zero however generous the policy.