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//! Tools for determining what circuits to preemptively build.
use crate::{PathConfig, PreemptiveCircuitConfig, TargetCircUsage, TargetPort};
use std::collections::HashMap;
use std::sync::Arc;
use std::time::Instant;
use tracing::warn;
/// Predicts what circuits might be used in future based on past activity, and suggests
/// circuits to preemptively build as a result.
pub(crate) struct PreemptiveCircuitPredictor {
/// A map of every exit port we've observed being used (or `None` if we observed an exit being
/// used to resolve DNS names instead of building a stream), to the last time we encountered
/// such usage.
// TODO(nickm): Let's have a mechanism for cleaning this out from time to time.
usages: HashMap<Option<TargetPort>, Instant>,
/// Configuration for this predictor.
config: tor_config::MutCfg<PreemptiveCircuitConfig>,
}
impl PreemptiveCircuitPredictor {
/// Create a new predictor, starting out with a set of ports we think are likely to be used.
pub(crate) fn new(config: PreemptiveCircuitConfig) -> Self {
let mut usages = HashMap::new();
for port in &config.initial_predicted_ports {
// TODO(nickm) should this be IPv6? Should we have a way to configure IPv6 initial ports?
usages.insert(Some(TargetPort::ipv4(*port)), Instant::now());
// We want to build circuits for resolving DNS, too.
usages.insert(None, Instant::now());
Self {
usages,
config: config.into(),
/// Return the configuration for this PreemptiveCircuitPredictor.
pub(crate) fn config(&self) -> Arc<PreemptiveCircuitConfig> {
self.config.get()
/// Replace the current configuration for this PreemptiveCircuitPredictor
/// with `new_config`.
pub(crate) fn set_config(&self, mut new_config: PreemptiveCircuitConfig) {
self.config.map_and_replace(|cfg| {
// Force this to stay the same, since it can't meaningfully be changed.
new_config
.initial_predicted_ports
.clone_from(&cfg.initial_predicted_ports);
});
/// Make some predictions for what circuits should be built.
pub(crate) fn predict(&self, path_config: &PathConfig) -> Vec<TargetCircUsage> {
let config = self.config();
let now = Instant::now();
let circs = config.min_exit_circs_for_port;
self.usages
.iter()
.filter(|(_, &time)| {
time.checked_add(config.prediction_lifetime)
.map(|t| t > now)
.unwrap_or_else(|| {
// FIXME(eta): this is going to be a bit noisy if it triggers, but that's better
// than panicking or silently doing the wrong thing?
warn!("failed to represent preemptive circuit prediction lifetime as an Instant");
false
})
.map(|(&port, _)| {
let require_stability = port.is_some_and(|p| path_config.long_lived_ports.contains(&p.port));
TargetCircUsage::Preemptive {
port, circs, require_stability,
.collect()
/// Note the use of a new port at the provided `time`.
///
/// # Limitations
/// This function assumes that the `time` values it receives are
/// monotonically increasing.
pub(crate) fn note_usage(&mut self, port: Option<TargetPort>, time: Instant) {
self.usages.insert(port, time);
#[cfg(test)]
mod test {
// @@ begin test lint list maintained by maint/add_warning @@
#![allow(clippy::bool_assert_comparison)]
#![allow(clippy::clone_on_copy)]
#![allow(clippy::dbg_macro)]
#![allow(clippy::mixed_attributes_style)]
#![allow(clippy::print_stderr)]
#![allow(clippy::print_stdout)]
#![allow(clippy::single_char_pattern)]
#![allow(clippy::unwrap_used)]
#![allow(clippy::unchecked_duration_subtraction)]
#![allow(clippy::useless_vec)]
#![allow(clippy::needless_pass_by_value)]
//! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
use crate::{
PathConfig, PreemptiveCircuitConfig, PreemptiveCircuitPredictor, TargetCircUsage,
TargetPort,
};
use std::time::{Duration, Instant};
use crate::isolation::test::{assert_isoleq, IsolationTokenEq};
#[test]
fn predicts_starting_ports() {
let path_config = PathConfig::default();
let mut cfg = PreemptiveCircuitConfig::builder();
cfg.set_initial_predicted_ports(vec![]);
cfg.prediction_lifetime(Duration::from_secs(2));
let predictor = PreemptiveCircuitPredictor::new(cfg.build().unwrap());
assert_isoleq!(
predictor.predict(&path_config),
vec![TargetCircUsage::Preemptive {
port: None,
circs: 2,
require_stability: false,
}]
);
cfg.set_initial_predicted_ports(vec![80]);
let results = predictor.predict(&path_config);
assert_eq!(results.len(), 2);
assert!(results
.any(|r| r.isol_eq(&TargetCircUsage::Preemptive {
})));
port: Some(TargetPort::ipv4(80)),
fn predicts_used_ports() {
let mut predictor = PreemptiveCircuitPredictor::new(cfg.build().unwrap());
predictor.note_usage(Some(TargetPort::ipv4(1234)), Instant::now());
port: Some(TargetPort::ipv4(1234)),
fn does_not_predict_old_ports() {
let three_seconds_ago = now - Duration::from_secs(2 + 1);
predictor.note_usage(Some(TargetPort::ipv4(2345)), three_seconds_ago);