// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.net.neighbor;

using zx;

/// Neighbor table entry state.
///
/// Modeled after RFC 4861 section 7.3.2. Descriptions are kept
/// implementation-independent by using a set of generic terminology.
///
/// ,------------------------------------------------------------------.
/// | Generic Term              | ARP Term    | NDP Term               |
/// |---------------------------+-------------+------------------------|
/// | Reachability Probe        | ARP Request | Neighbor Solicitation  |
/// | Reachability Confirmation | ARP Reply   | Neighbor Advertisement |
/// `---------------------------+-------------+------------------------'
flexible union EntryState {
    /// Reachability is in the process of being confirmed for a newly created,
    /// non-static entry.
    1: IncompleteState incomplete;

    /// Positive reachability has been confirmed; the path to the neighbor is
    /// functioning properly.
    2: ReachableState reachable;

    /// Reachability is considered unknown.
    ///
    /// Occurs in one of two ways:
    ///   1. Too much time has elapsed since the last positive reachability
    ///      confirmation was received.
    ///   2. Received a reachability confirmation from a neighbor with a
    ///      different MAC address than the one cached.
    3: StaleState stale;

    /// A packet was recently sent while reachability was considered unknown.
    ///
    /// This state is an optimization that gives non-Neighbor-Discovery related
    /// protocols time to confirm reachability after the last confirmation of
    /// reachability has expired due to lack of recent traffic.
    4: DelayState delay;

    /// A reachability confirmation is actively sought by periodically
    /// retransmitting reachability probes until a reachability confirmation is
    /// received, or until the max amount of probes has been sent.
    5: ProbeState probe;

    /// Static entries are explicitly added with [`Controller.AddEntry`]. They
    /// do not expire and are not deleted until explicitly removed with
    /// [`Controller.RemoveEntry`].
    6: StaticState static;
};

table IncompleteState {
};

table ReachableState {
    /// When reachability expires and the entry should be considered stale; when
    /// to transition from `reachable` to `stale` [`EntryState`].
    ///
    /// This is not the only way to transition into [`EntryState.stale`]. The
    /// entry will transition into `stale` before this time when an unsolicited
    /// reachability confirmation is received with a different MAC address than
    /// the one cached.
    1: zx.time expires_at;
};

table StaleState {
};

table DelayState {
};

table ProbeState {
};

table StaticState {
};