//! Utilities for scoring payment channels.
//!
-//! [`Scorer`] may be given to [`get_route`] to score payment channels during path finding when a
+//! [`Scorer`] may be given to [`find_route`] to score payment channels during path finding when a
//! custom [`routing::Score`] implementation is not needed.
//!
//! # Example
//! # extern crate secp256k1;
//! #
//! # use lightning::routing::network_graph::NetworkGraph;
-//! # use lightning::routing::router::get_route;
-//! # use lightning::routing::scorer::Scorer;
+//! # use lightning::routing::router::{RouteParameters, find_route};
+//! # use lightning::routing::scorer::{Scorer, ScoringParameters};
//! # use lightning::util::logger::{Logger, Record};
//! # use secp256k1::key::PublicKey;
//! #
//! # impl Logger for FakeLogger {
//! # fn log(&self, record: &Record) { unimplemented!() }
//! # }
-//! # fn find_scored_route(payer: PublicKey, payee: PublicKey, network_graph: NetworkGraph) {
+//! # fn find_scored_route(payer: PublicKey, params: RouteParameters, network_graph: NetworkGraph) {
//! # let logger = FakeLogger {};
//! #
-//! // Use the default channel penalty.
+//! // Use the default channel penalties.
//! let scorer = Scorer::default();
//!
-//! // Or use a custom channel penalty.
-//! let scorer = Scorer::new(1_000);
+//! // Or use custom channel penalties.
+//! let scorer = Scorer::new(ScoringParameters {
+//! base_penalty_msat: 1000,
+//! failure_penalty_msat: 2 * 1024 * 1000,
+//! ..ScoringParameters::default()
+//! });
//!
-//! let route = get_route(&payer, &network_graph, &payee, None, None, &vec![], 1_000, 42, &logger, &scorer);
+//! let route = find_route(&payer, ¶ms, &network_graph, None, &logger, &scorer);
//! # }
//! ```
//!
-//! [`get_route`]: crate::routing::router::get_route
+//! # Note
+//!
+//! If persisting [`Scorer`], it must be restored using the same [`Time`] parameterization. Using a
+//! different type results in undefined behavior. Specifically, persisting when built with feature
+//! `no-std` and restoring without it, or vice versa, uses different types and thus is undefined.
+//!
+//! [`find_route`]: crate::routing::router::find_route
use routing;
+use ln::msgs::DecodeError;
+use routing::network_graph::NodeId;
+use routing::router::RouteHop;
+use util::ser::{Readable, Writeable, Writer};
+
+use prelude::*;
+use core::ops::Sub;
+use core::time::Duration;
+use io::{self, Read};
+
/// [`routing::Score`] implementation that provides reasonable default behavior.
///
/// Used to apply a fixed penalty to each channel, thus avoiding long paths when shorter paths with
-/// slightly higher fees are available.
+/// slightly higher fees are available. Will further penalize channels that fail to relay payments.
///
/// See [module-level documentation] for usage.
///
/// [module-level documentation]: crate::routing::scorer
-pub struct Scorer {
- base_penalty_msat: u64,
+pub type Scorer = ScorerUsingTime::<DefaultTime>;
+
+/// Time used by [`Scorer`].
+#[cfg(not(feature = "no-std"))]
+pub type DefaultTime = std::time::Instant;
+
+/// Time used by [`Scorer`].
+#[cfg(feature = "no-std")]
+pub type DefaultTime = Eternity;
+
+/// [`routing::Score`] implementation parameterized by [`Time`].
+///
+/// See [`Scorer`] for details.
+///
+/// # Note
+///
+/// Mixing [`Time`] types between serialization and deserialization results in undefined behavior.
+pub struct ScorerUsingTime<T: Time> {
+ params: ScoringParameters,
+ // TODO: Remove entries of closed channels.
+ channel_failures: HashMap<u64, ChannelFailure<T>>,
+}
+
+/// Parameters for configuring [`Scorer`].
+pub struct ScoringParameters {
+ /// A fixed penalty in msats to apply to each channel.
+ pub base_penalty_msat: u64,
+
+ /// A penalty in msats to apply to a channel upon failing to relay a payment.
+ ///
+ /// This accumulates for each failure but may be reduced over time based on
+ /// [`failure_penalty_half_life`].
+ ///
+ /// [`failure_penalty_half_life`]: Self::failure_penalty_half_life
+ pub failure_penalty_msat: u64,
+
+ /// The time required to elapse before any accumulated [`failure_penalty_msat`] penalties are
+ /// cut in half.
+ ///
+ /// # Note
+ ///
+ /// When time is an [`Eternity`], as is default when enabling feature `no-std`, it will never
+ /// elapse. Therefore, this penalty will never decay.
+ ///
+ /// [`failure_penalty_msat`]: Self::failure_penalty_msat
+ pub failure_penalty_half_life: Duration,
+}
+
+impl_writeable_tlv_based!(ScoringParameters, {
+ (0, base_penalty_msat, required),
+ (2, failure_penalty_msat, required),
+ (4, failure_penalty_half_life, required),
+});
+
+/// Accounting for penalties against a channel for failing to relay any payments.
+///
+/// Penalties decay over time, though accumulate as more failures occur.
+struct ChannelFailure<T: Time> {
+ /// Accumulated penalty in msats for the channel as of `last_failed`.
+ undecayed_penalty_msat: u64,
+
+ /// Last time the channel failed. Used to decay `undecayed_penalty_msat`.
+ last_failed: T,
+}
+
+/// A measurement of time.
+pub trait Time: Sub<Duration, Output = Self> where Self: Sized {
+ /// Returns an instance corresponding to the current moment.
+ fn now() -> Self;
+
+ /// Returns the amount of time elapsed since `self` was created.
+ fn elapsed(&self) -> Duration;
+
+ /// Returns the amount of time passed since the beginning of [`Time`].
+ ///
+ /// Used during (de-)serialization.
+ fn duration_since_epoch() -> Duration;
}
-impl Scorer {
- /// Creates a new scorer using `base_penalty_msat` as the channel penalty.
- pub fn new(base_penalty_msat: u64) -> Self {
- Self { base_penalty_msat }
+impl<T: Time> ScorerUsingTime<T> {
+ /// Creates a new scorer using the given scoring parameters.
+ pub fn new(params: ScoringParameters) -> Self {
+ Self {
+ params,
+ channel_failures: HashMap::new(),
+ }
+ }
+
+ /// Creates a new scorer using `penalty_msat` as a fixed channel penalty.
+ #[cfg(any(test, feature = "fuzztarget", feature = "_test_utils"))]
+ pub fn with_fixed_penalty(penalty_msat: u64) -> Self {
+ Self::new(ScoringParameters {
+ base_penalty_msat: penalty_msat,
+ failure_penalty_msat: 0,
+ failure_penalty_half_life: Duration::from_secs(0),
+ })
+ }
+}
+
+impl<T: Time> ChannelFailure<T> {
+ fn new(failure_penalty_msat: u64) -> Self {
+ Self {
+ undecayed_penalty_msat: failure_penalty_msat,
+ last_failed: T::now(),
+ }
+ }
+
+ fn add_penalty(&mut self, failure_penalty_msat: u64, half_life: Duration) {
+ self.undecayed_penalty_msat = self.decayed_penalty_msat(half_life) + failure_penalty_msat;
+ self.last_failed = T::now();
+ }
+
+ fn decayed_penalty_msat(&self, half_life: Duration) -> u64 {
+ let decays = self.last_failed.elapsed().as_secs().checked_div(half_life.as_secs());
+ match decays {
+ Some(decays) => self.undecayed_penalty_msat >> decays,
+ None => 0,
+ }
+ }
+}
+
+impl<T: Time> Default for ScorerUsingTime<T> {
+ fn default() -> Self {
+ Self::new(ScoringParameters::default())
}
}
-impl Default for Scorer {
- /// Creates a new scorer using 500 msat as the channel penalty.
+impl Default for ScoringParameters {
fn default() -> Self {
- Scorer::new(500)
+ Self {
+ base_penalty_msat: 500,
+ failure_penalty_msat: 1024 * 1000,
+ failure_penalty_half_life: Duration::from_secs(3600),
+ }
+ }
+}
+
+impl<T: Time> routing::Score for ScorerUsingTime<T> {
+ fn channel_penalty_msat(
+ &self, short_channel_id: u64, _source: &NodeId, _target: &NodeId
+ ) -> u64 {
+ let failure_penalty_msat = self.channel_failures
+ .get(&short_channel_id)
+ .map_or(0, |value| value.decayed_penalty_msat(self.params.failure_penalty_half_life));
+
+ self.params.base_penalty_msat + failure_penalty_msat
+ }
+
+ fn payment_path_failed(&mut self, _path: &[&RouteHop], short_channel_id: u64) {
+ let failure_penalty_msat = self.params.failure_penalty_msat;
+ let half_life = self.params.failure_penalty_half_life;
+ self.channel_failures
+ .entry(short_channel_id)
+ .and_modify(|failure| failure.add_penalty(failure_penalty_msat, half_life))
+ .or_insert_with(|| ChannelFailure::new(failure_penalty_msat));
+ }
+}
+
+#[cfg(not(feature = "no-std"))]
+impl Time for std::time::Instant {
+ fn now() -> Self {
+ std::time::Instant::now()
+ }
+
+ fn duration_since_epoch() -> Duration {
+ use std::time::SystemTime;
+ SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap()
+ }
+
+ fn elapsed(&self) -> Duration {
+ std::time::Instant::elapsed(self)
+ }
+}
+
+/// A state in which time has no meaning.
+#[derive(Debug, PartialEq, Eq)]
+pub struct Eternity;
+
+impl Time for Eternity {
+ fn now() -> Self {
+ Self
+ }
+
+ fn duration_since_epoch() -> Duration {
+ Duration::from_secs(0)
+ }
+
+ fn elapsed(&self) -> Duration {
+ Duration::from_secs(0)
+ }
+}
+
+impl Sub<Duration> for Eternity {
+ type Output = Self;
+
+ fn sub(self, _other: Duration) -> Self {
+ self
+ }
+}
+
+impl<T: Time> Writeable for ScorerUsingTime<T> {
+ #[inline]
+ fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+ self.params.write(w)?;
+ self.channel_failures.write(w)?;
+ write_tlv_fields!(w, {});
+ Ok(())
+ }
+}
+
+impl<T: Time> Readable for ScorerUsingTime<T> {
+ #[inline]
+ fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
+ let res = Ok(Self {
+ params: Readable::read(r)?,
+ channel_failures: Readable::read(r)?,
+ });
+ read_tlv_fields!(r, {});
+ res
+ }
+}
+
+impl<T: Time> Writeable for ChannelFailure<T> {
+ #[inline]
+ fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+ let duration_since_epoch = T::duration_since_epoch() - self.last_failed.elapsed();
+ write_tlv_fields!(w, {
+ (0, self.undecayed_penalty_msat, required),
+ (2, duration_since_epoch, required),
+ });
+ Ok(())
}
}
-impl routing::Score for Scorer {
- fn channel_penalty_msat(&self, _short_channel_id: u64) -> u64 { self.base_penalty_msat }
+impl<T: Time> Readable for ChannelFailure<T> {
+ #[inline]
+ fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
+ let mut undecayed_penalty_msat = 0;
+ let mut duration_since_epoch = Duration::from_secs(0);
+ read_tlv_fields!(r, {
+ (0, undecayed_penalty_msat, required),
+ (2, duration_since_epoch, required),
+ });
+ Ok(Self {
+ undecayed_penalty_msat,
+ last_failed: T::now() - (T::duration_since_epoch() - duration_since_epoch),
+ })
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::{Eternity, ScoringParameters, ScorerUsingTime, Time};
+
+ use routing::Score;
+ use routing::network_graph::NodeId;
+
+ use bitcoin::secp256k1::PublicKey;
+ use core::cell::Cell;
+ use core::ops::Sub;
+ use core::time::Duration;
+
+ /// Time that can be advanced manually in tests.
+ #[derive(Debug, PartialEq, Eq)]
+ struct SinceEpoch(Duration);
+
+ impl SinceEpoch {
+ thread_local! {
+ static ELAPSED: Cell<Duration> = core::cell::Cell::new(Duration::from_secs(0));
+ }
+
+ fn advance(duration: Duration) {
+ Self::ELAPSED.with(|elapsed| elapsed.set(elapsed.get() + duration))
+ }
+ }
+
+ impl Time for SinceEpoch {
+ fn now() -> Self {
+ Self(Self::duration_since_epoch())
+ }
+
+ fn duration_since_epoch() -> Duration {
+ Self::ELAPSED.with(|elapsed| elapsed.get())
+ }
+
+ fn elapsed(&self) -> Duration {
+ Self::duration_since_epoch() - self.0
+ }
+ }
+
+ impl Sub<Duration> for SinceEpoch {
+ type Output = Self;
+
+ fn sub(self, other: Duration) -> Self {
+ Self(self.0 - other)
+ }
+ }
+
+ #[test]
+ fn time_passes_when_advanced() {
+ let now = SinceEpoch::now();
+ assert_eq!(now.elapsed(), Duration::from_secs(0));
+
+ SinceEpoch::advance(Duration::from_secs(1));
+ SinceEpoch::advance(Duration::from_secs(1));
+
+ let elapsed = now.elapsed();
+ let later = SinceEpoch::now();
+
+ assert_eq!(elapsed, Duration::from_secs(2));
+ assert_eq!(later - elapsed, now);
+ }
+
+ #[test]
+ fn time_never_passes_in_an_eternity() {
+ let now = Eternity::now();
+ let elapsed = now.elapsed();
+ let later = Eternity::now();
+
+ assert_eq!(now.elapsed(), Duration::from_secs(0));
+ assert_eq!(later - elapsed, now);
+ }
}
projects / rust-lightning / blobdiff