path: root/src/swarm/topology/tests.rs

use super::*;
use std::collections::VecDeque;

fn members(n: usize) -> Vec<String> {
    (0..n).map(|i| format!("{:064x}", i * 7919 + 13)).collect()
}

fn all_reachable(_: &str) -> bool {
    false
}

fn none_stable(_: &str) -> bool {
    false
}

fn graph(members: &[String], k: usize) -> BTreeMap<String, BTreeSet<String>> {
    super::graph(members, k, &all_reachable, &none_stable)
}

fn connected(g: &BTreeMap<String, BTreeSet<String>>) -> bool {
    let Some(start) = g.keys().next() else {
        return true;
    };
    let mut seen = BTreeSet::from([start.clone()]);
    let mut queue = VecDeque::from([start.clone()]);
    while let Some(m) = queue.pop_front() {
        for next in &g[&m] {
            if seen.insert(next.clone()) {
                queue.push_back(next.clone());
            }
        }
    }
    seen.len() == g.len()
}

fn edges(graph: &BTreeMap<String, BTreeSet<String>>) -> BTreeSet<(String, String)> {
    graph
        .iter()
        .flat_map(|(a, ns)| {
            ns.iter().map(move |b| {
                if a < b {
                    (a.clone(), b.clone())
                } else {
                    (b.clone(), a.clone())
                }
            })
        })
        .collect()
}

fn hex(bytes: [u8; 32]) -> String {
    crate::transport::Hex(&bytes).to_string()
}

/// Over random swarms (size, `k`, who is reachable, who is stable): links only
/// between reachable members, never to oneself, symmetric; a full mesh while small,
/// otherwise at least `k` links each and connected; independent of the order members
/// are listed in; and each member's own view (`neighbours`) agrees with the graph.
#[test]
fn random_swarms() {
    crate::testrand::for_seeds(300, |rng| {
        let n = rng.between(1, 60);
        let k = rng.between(2, 14);
        let mut all: Vec<String> = (0..n).map(|_| hex(rng.bytes32())).collect();
        let unreachable: BTreeSet<String> =
            all.iter().filter(|_| rng.chance(0.3)).cloned().collect();
        let stable: BTreeSet<String> = all.iter().filter(|_| rng.chance(0.3)).cloned().collect();
        let is_unreachable = |m: &str| unreachable.contains(m);
        let is_stable = |m: &str| stable.contains(m);

        let g = super::graph(&all, k, &is_unreachable, &is_stable);
        // Owned: `all` is shuffled below.
        let live: BTreeSet<String> = all
            .iter()
            .filter(|m| !unreachable.contains(*m))
            .cloned()
            .collect();
        assert_eq!(g.keys().cloned().collect::<BTreeSet<_>>(), live);
        for (a, ns) in &g {
            assert!(!ns.contains(a), "{a} links to itself");
            for b in ns {
                assert!(live.contains(b), "{a} links to unreachable {b}");
                assert!(g[b].contains(a), "{a} -> {b} but not back");
            }
        }
        if live.len() <= k + 1 {
            assert!(
                g.values().all(|ns| ns.len() + 1 == live.len()),
                "not a full mesh"
            );
        } else {
            assert!(
                g.values().all(|ns| ns.len() >= k),
                "a member with fewer than k links"
            );
            assert!(connected(&g), "not connected");
        }

        rng.shuffle(&mut all);
        assert_eq!(super::graph(&all, k, &is_unreachable, &is_stable), g);

        if let Some(local) = live.iter().nth(rng.below(live.len())) {
            let others: Vec<String> = all.iter().filter(|m| *m != local).cloned().collect();
            assert_eq!(
                neighbours(&others, local, k, &is_unreachable, &is_stable),
                g[local]
            );
        }
    });
}

#[test]
fn small_swarms_are_a_full_mesh() {
    let ms = members(13);
    for m in &ms {
        assert_eq!(
            neighbours(&ms, m, 12, &all_reachable, &none_stable).len(),
            12
        );
    }
}

#[test]
fn links_are_symmetric_and_degree_at_least_k() {
    let ms = members(250);
    let g = graph(&ms, 8);
    for (a, ns) in &g {
        assert!(ns.len() >= 8, "{a} has {} neighbours", ns.len());
        assert!(!ns.contains(a));
        for b in ns {
            assert!(g[b].contains(a), "{a} -> {b} not symmetric");
        }
    }
}

#[test]
fn graph_is_connected() {
    for (n, k) in [(250, 8), (250, 2), (60, 3)] {
        assert!(connected(&graph(&members(n), k)), "n={n} k={k}");
    }
}

#[test]
fn one_member_joining_changes_few_links() {
    let ms = members(200);
    let before = edges(&graph(&ms, 8));
    let mut more = ms.clone();
    more.push(format!("{:064x}", 999_999));
    let after = edges(&graph(&more, 8));
    let changed = before.symmetric_difference(&after).count();
    assert!(changed <= 4 * 8, "{changed} links changed");
}

#[test]
fn reachable_members_stay_connected_when_most_are_offline() {
    let ms = members(100);
    // Every tenth member is online.
    let online: BTreeSet<String> = ms.iter().step_by(10).cloned().collect();
    let offline = |m: &str| !online.contains(m);
    let g = super::graph(&ms, 12, &offline, &none_stable);
    assert_eq!(g.len(), 10);
    // Ten reachable members and k = 12: a full mesh among them.
    assert!(g.values().all(|ns| ns.len() == 9));

    let online: BTreeSet<String> = ms.iter().step_by(4).cloned().collect();
    let offline = |m: &str| !online.contains(m);
    let g = super::graph(&ms, 8, &offline, &none_stable);
    assert_eq!(g.len(), 25);
    assert!(connected(&g));
    assert!(
        g.values()
            .all(|ns| ns.len() >= 8 && ns.iter().all(|n| online.contains(n)))
    );
}

#[test]
fn stable_members_become_hubs_with_bounded_degree() {
    let ms = members(250);
    let stable: BTreeSet<String> = ms.iter().step_by(12).take(20).cloned().collect();
    let is_stable = |m: &str| stable.contains(m);
    let g = super::graph(&ms, 12, &all_reachable, &is_stable);
    assert!(connected(&g));

    let degree = |pred: &dyn Fn(&String) -> bool| -> (usize, f64) {
        let degrees: Vec<usize> = g
            .iter()
            .filter(|(m, _)| pred(m))
            .map(|(_, ns)| ns.len())
            .collect();
        let max = *degrees.iter().max().unwrap();
        (
            max,
            degrees.iter().sum::<usize>() as f64 / degrees.len() as f64,
        )
    };
    let (stable_max, stable_mean) = degree(&|m| stable.contains(m));
    let (_, transient_mean) = degree(&|m| !stable.contains(m));
    // 230 transient members put about 5 of their 10 scored slots on 20 stable ones.
    assert!(
        stable_mean > 3.0 * transient_mean,
        "{stable_mean} vs {transient_mean}"
    );
    assert!(
        stable_max <= 100,
        "a stable member has {stable_max} neighbours"
    );
}

/// A hub's degree in a swarm of `n` with `stable_count` stable members stays within
/// the bound.
fn hub_degree_is_bounded(n: usize, stable_count: usize) {
    // Few stable members among many: without the fan-in budget each would be chosen
    // by most of the swarm (about 130 neighbours with 10 of 250). With it, a hub has
    // at most the budget plus the links others choose by pair score and the ring.
    let k = 12;
    let ms = members(n);
    let stable: BTreeSet<String> = ms.iter().step_by(n / stable_count).cloned().collect();
    let is_stable = |m: &str| stable.contains(m);
    let g = super::graph(&ms, k, &all_reachable, &is_stable);
    assert!(connected(&g), "n={n} stable={stable_count}");
    let hub_max = g
        .iter()
        .filter(|(m, _)| stable.contains(*m))
        .map(|(_, ns)| ns.len())
        .max()
        .unwrap();
    assert!(
        hub_max <= 8 * k,
        "n={n} stable={stable_count}: a stable member has {hub_max} neighbours"
    );
}

/// Two transports with members on one or the other, and two members on both: every
/// link is over a shared transport, and the two members on both connect the rest.
#[test]
fn members_on_two_transports_bridge_the_others() {
    let k = 8;
    let ms = members(201);
    let on = |names: &[&str]| -> BTreeSet<String> {
        names.iter().map(|name| (*name).to_owned()).collect()
    };
    let transports: BTreeMap<String, BTreeSet<String>> = ms
        .iter()
        .enumerate()
        .map(|(i, m)| {
            let transports = match i {
                0 | 1 => on(&["a", "b"]),
                i if i % 2 == 0 => on(&["a"]),
                _ => on(&["b"]),
            };
            (m.clone(), transports)
        })
        .collect();
    let no_stable = |_: &str| false;
    let mut graph: BTreeMap<String, BTreeSet<String>> = BTreeMap::new();
    for (m, own) in &transports {
        for n in neighbours_across(&transports, m, own, k, &all_reachable, &no_stable) {
            assert!(
                !transports[&n].is_disjoint(own),
                "{m} and {n} share no transport"
            );
            graph.entry(m.clone()).or_default().insert(n.clone());
            graph.entry(n).or_default().insert(m.clone());
        }
    }
    assert_eq!(graph.len(), ms.len());
    assert!(connected(&graph));
    let bridge = &ms[0];
    assert!(graph[bridge].iter().any(|n| !transports[n].contains("b")));
    assert!(graph[bridge].iter().any(|n| !transports[n].contains("a")));

    // One transport: the one graph, as without transports.
    let one: BTreeMap<String, BTreeSet<String>> =
        ms.iter().map(|m| (m.clone(), on(&[""]))).collect();
    for m in &ms[..5] {
        assert_eq!(
            neighbours_across(&one, m, &on(&[""]), k, &all_reachable, &no_stable),
            neighbours(&ms, m, k, &all_reachable, &no_stable)
        );
    }
}

#[test]
fn schemes_of_addresses() {
    let addresses = |all: &[&str]| -> Vec<String> { all.iter().map(|a| (*a).to_owned()).collect() };
    assert_eq!(
        schemes(&addresses(&[
            "mycelium:ab",
            "libp2p:/ip4/1.2.3.4/tcp/1",
            "libp2p:/ip6/::1/tcp/1"
        ])),
        BTreeSet::from(["libp2p".to_owned(), "mycelium".to_owned()])
    );
    assert_eq!(schemes(&addresses(&["a"])), BTreeSet::from([String::new()]));
    assert!(schemes(&[]).is_empty());
}

#[test]
fn hub_degree_is_bounded_however_few_stable_members() {
    for (n, stable_count) in [(250, 10), (400, 5)] {
        hub_degree_is_bounded(n, stable_count);
    }
}

/// The same at the sizes the bound was designed for; slow in debug builds, so run
/// on request (`cargo test --release -- --ignored`).
#[test]
#[ignore]
fn hub_degree_is_bounded_in_large_swarms() {
    for (n, stable_count) in [(1000, 10), (1000, 20), (2000, 20)] {
        hub_degree_is_bounded(n, stable_count);
    }
}