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//! Vanguard sets
use std::cmp;
use std::time::{Duration, SystemTime};
use derive_deftly::Deftly;
use rand::seq::IndexedRandom as _;
use serde::{Deserialize, Serialize};
use tor_basic_utils::RngExt as _;
use tor_error::internal;
use tor_linkspec::{HasRelayIds as _, RelayIdSet, RelayIds};
use tor_netdir::{NetDir, Relay};
use tor_relay_selection::{LowLevelRelayPredicate as _, RelayExclusion, RelaySelector, RelayUsage};
use tor_rtcompat::Runtime;
use tracing::{debug, trace};
#[cfg(test)]
use derive_deftly::derive_deftly_adhoc;
use crate::{VanguardMgrError, VanguardMode};
use super::VanguardParams;
/// A vanguard relay.
#[derive(Clone, amplify::Getters)]
pub struct Vanguard<'a> {
/// The relay.
relay: Relay<'a>,
}
/// An identifier for a time-bound vanguard.
///
/// Each vanguard [`Layer`](crate::vanguards::Layer) consists of a [`VanguardSet`],
/// which contains multiple `TimeBoundVanguard`s.
/// A [`VanguardSet`]'s `TimeBoundVanguard`s are rotated
/// by [`VanguardMgr`](crate::vanguards::VanguardMgr) as soon as they expire.
/// If [Full](crate::vanguards::VanguardMode) vanguards are in use,
/// the `TimeBoundVanguard`s from all layers are persisted to disk.
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)] //
pub(crate) struct TimeBoundVanguard {
/// The ID of this relay.
pub(super) id: RelayIds,
/// When to stop using this relay as a vanguard.
pub(super) when: SystemTime,
/// A set of vanguards, for use in a particular [`Layer`](crate::vanguards::Layer).
/// `VanguardSet`s start out with a target size of `0`.
/// Upon obtaining a `NetDir`, users of this type should update the target
/// based on the current [`NetParameters`](tor_netdir::params::NetParameters).
#[derive(Default, Debug, Clone, PartialEq)] //
#[derive(Serialize, Deserialize)] //
#[serde(transparent)]
pub(super) struct VanguardSet {
/// The time-bound vanguards of a given [`Layer`](crate::vanguards::Layer).
vanguards: Vec<TimeBoundVanguard>,
/// The number of vanguards we would like to have in this set.
/// We do not serialize this value, as it should be derived from, and kept up to date with,
/// the current [`NetParameters`](tor_netdir::params::NetParameters).
#[serde(skip)]
target: usize,
/// The L2 and L3 vanguard sets,
/// stored in the same struct to simplify serialization.
#[derive(Deftly, Serialize, Deserialize)] //
#[derive_deftly_adhoc]
pub(super) struct VanguardSets {
/// The L2 vanguard sets.
l2_vanguards: VanguardSet,
/// The L3 vanguard sets.
/// Only used if full vanguards are enabled.
l3_vanguards: VanguardSet,
impl VanguardSets {
/// Find the timestamp of the vanguard that is due to expire next.
pub(super) fn next_expiry(&self) -> Option<SystemTime> {
let l2_expiry = self.l2_vanguards.next_expiry();
let l3_expiry = self.l3_vanguards.next_expiry();
match (l2_expiry, l3_expiry) {
(Some(e), None) | (None, Some(e)) => Some(e),
(Some(e1), Some(e2)) => Some(cmp::min(e1, e2)),
(None, None) => {
// Both vanguard sets are empty
None
/// Return a reference to the L2 [`VanguardSet`].
pub(super) fn l2(&self) -> &VanguardSet {
&self.l2_vanguards
/// Return a reference to the L3 [`VanguardSet`].
pub(super) fn l3(&self) -> &VanguardSet {
&self.l3_vanguards
/// Remove the vanguards that are expired at the specified timestamp.
/// Returns the number of vanguards that were removed.
pub(super) fn remove_expired(&mut self, now: SystemTime) -> usize {
let l2_expired = self.l2_vanguards.remove_expired(now);
let l3_expired = self.l3_vanguards.remove_expired(now);
l2_expired + l3_expired
/// Remove the vanguards that are no longer listed in `netdir`.
/// Returns whether either of the two sets have changed.
pub(super) fn remove_unlisted(&mut self, netdir: &NetDir) {
self.l2_vanguards.remove_unlisted(netdir);
self.l3_vanguards.remove_unlisted(netdir);
/// Replenish the vanguard sets if necessary, using the directory information
/// from the specified [`NetDir`].
/// Note: the L3 set is only replenished if [`Full`](VanguardMode::Full) vanguards are enabled.
pub(super) fn replenish_vanguards<R: Runtime>(
&mut self,
runtime: &R,
netdir: &NetDir,
params: &VanguardParams,
mode: VanguardMode,
) -> Result<(), VanguardMgrError> {
trace!("Replenishing vanguard sets");
// Resize the vanguard sets if necessary.
self.l2_vanguards.update_target(params.l2_pool_size());
let mut rng = rand::rng();
Self::replenish_set(
runtime,
&mut rng,
netdir,
&mut self.l2_vanguards,
params.l2_lifetime_min(),
params.l2_lifetime_max(),
)?;
if mode == VanguardMode::Full {
self.l3_vanguards.update_target(params.l3_pool_size());
&mut self.l3_vanguards,
params.l3_lifetime_min(),
params.l3_lifetime_max(),
Ok(())
/// Replenish a single `VanguardSet` with however many vanguards it is short of.
fn replenish_set<R: Runtime, Rng: rand::Rng>(
rng: &mut Rng,
vanguard_set: &mut VanguardSet,
min_lifetime: Duration,
max_lifetime: Duration,
) -> Result<bool, VanguardMgrError> {
let mut set_changed = false;
let deficit = vanguard_set.deficit();
if deficit > 0 {
// Exclude the relays that are already in this vanguard set.
let exclude_ids = RelayIdSet::from(&*vanguard_set);
let exclude = RelayExclusion::exclude_identities(exclude_ids);
// Pick some vanguards to add to the vanguard_set.
let new_vanguards = Self::add_n_vanguards(
rng,
deficit,
exclude,
min_lifetime,
max_lifetime,
if !new_vanguards.is_empty() {
set_changed = true;
for v in new_vanguards {
vanguard_set.add_vanguard(v);
Ok(set_changed)
/// Select `n` relays to use as vanguards.
/// Each selected vanguard will have a random lifetime
/// between `min_lifetime` and `max_lifetime`.
fn add_n_vanguards<R: Runtime, Rng: rand::Rng>(
n: usize,
exclude: RelayExclusion,
) -> Result<Vec<TimeBoundVanguard>, VanguardMgrError> {
trace!(relay_count = n, "selecting relays to use as vanguards");
let vanguard_sel = RelaySelector::new(RelayUsage::vanguard(), exclude);
let (relays, _outcome) = vanguard_sel.select_n_relays(rng, n, netdir);
relays
.into_iter()
.map(|relay| {
// Pick an expiration for this vanguard.
let duration = select_lifetime(rng, min_lifetime, max_lifetime)?;
let when = runtime.wallclock() + duration;
Ok(TimeBoundVanguard {
id: RelayIds::from_relay_ids(&relay),
when,
})
.collect::<Result<Vec<_>, _>>()
/// Randomly select the lifetime of a vanguard from the `max(X,X)` distribution,
/// where `X` is a uniform random value between `min_lifetime` and `max_lifetime`.
/// This ensures we are biased towards longer lifetimes.
/// See
/// <https://spec.torproject.org/vanguards-spec/vanguards-stats.html>
//
// Note: the lifetimes of the vanguards (both L2 and L3) are selected
// from the max(X,X) distribution.
fn select_lifetime<Rng: rand::Rng>(
) -> Result<Duration, VanguardMgrError> {
let err = || internal!("invalid consensus: vanguard min_lifetime > max_lifetime");
let l1 = rng
.gen_range_checked(min_lifetime..=max_lifetime)
.ok_or_else(err)?;
let l2 = rng
Ok(std::cmp::max(l1, l2))
impl VanguardSet {
/// Pick a relay from this set.
/// See [`VanguardMgr::select_vanguard`](crate::vanguards::VanguardMgr::select_vanguard)
/// for more information.
pub(super) fn pick_relay<'a, R: rand::Rng>(
&self,
rng: &mut R,
netdir: &'a NetDir,
relay_selector: &RelaySelector<'a>,
) -> Option<Vanguard<'a>> {
let good_relays = self
.vanguards
.iter()
.filter_map(|vanguard| {
// Skip over any unusable relays
let relay = netdir.by_ids(&vanguard.id)?;
relay_selector
.low_level_predicate_permits_relay(&relay)
.then_some(relay)
.collect::<Vec<_>>();
// Note: We make a uniform choice instead of a weighted one,
// because we already made a bandwidth-weighted choice when we added
// the vanguards to this set in the first place.
good_relays.choose(rng).map(|relay| Vanguard {
relay: relay.clone(),
/// Whether this vanguard set is empty.
pub(super) fn is_empty(&self) -> bool {
self.vanguards.is_empty()
/// The number of vanguards we're missing.
fn deficit(&self) -> usize {
self.target.saturating_sub(self.vanguards.len())
/// Add a vanguard to this set.
fn add_vanguard(&mut self, v: TimeBoundVanguard) {
self.vanguards.push(v);
/// Remove the vanguards that are no longer listed in `netdir`
/// Returns the number of vanguards that were unlisted.
fn remove_unlisted(&mut self, netdir: &NetDir) -> usize {
self.retain(|v| {
let cond = netdir.ids_listed(&v.id) != Some(false);
if !cond {
debug!(id=?v.id, "Removing newly-unlisted vanguard");
cond
/// Returns the number of vanguards that expired.
fn remove_expired(&mut self, now: SystemTime) -> usize {
let cond = v.when > now;
debug!(id=?v.id, "Removing expired vanguard");
/// A wrapper around [`Vec::retain`] that returns the number of discarded elements.
fn retain<F>(&mut self, f: F) -> usize
where
F: FnMut(&TimeBoundVanguard) -> bool,
{
let old_len = self.vanguards.len();
self.vanguards.retain(f);
old_len - self.vanguards.len()
fn next_expiry(&self) -> Option<SystemTime> {
self.vanguards.iter().map(|v| v.when).min()
/// Update the target size of this set, discarding or requesting additional vanguards if needed.
fn update_target(&mut self, target: usize) {
self.target = target;
impl From<&VanguardSet> for RelayIdSet {
fn from(vanguard_set: &VanguardSet) -> Self {
vanguard_set
.flat_map(|vanguard| {
vanguard
.id
.clone()
.identities()
.map(|id| id.to_owned())
.collect::<Vec<_>>()
.collect()
// Some accessors we need in the VanguardMgr tests.
derive_deftly_adhoc! {
VanguardSets expect items:
$(
#[doc = concat!("Return the ", stringify!($fname))]
pub(super) fn $fname(&self) -> &Vec<TimeBoundVanguard> {
&self.$fname.vanguards
#[doc = concat!("Return the target size of the ", stringify!($fname), " set")]
pub(super) fn $<$fname _target>(&self) -> usize {
self.$fname.target
#[doc = concat!("Return the deficit of the ", stringify!($fname), " set")]
pub(super) fn $<$fname _deficit>(&self) -> usize {
self.$fname.deficit()
)