Merge pull request #1227 from jkczyz/2021-12-probabilistic-scorer
[rust-lightning] / lightning / src / routing / scoring.rs
index 20a8afcabcf827298229cb44ff9903cbc000c9f6..b02b61fa9f6c0381fe9fd7ffcad4eedd23656be5 100644 (file)
@@ -9,8 +9,8 @@
 
 //! Utilities for scoring payment channels.
 //!
-//! [`Scorer`] may be given to [`find_route`] to score payment channels during path finding when a
-//! custom [`Score`] implementation is not needed.
+//! [`ProbabilisticScorer`] may be given to [`find_route`] to score payment channels during path
+//! finding when a custom [`Score`] implementation is not needed.
 //!
 //! # Example
 //!
@@ -19,7 +19,7 @@
 //! #
 //! # use lightning::routing::network_graph::NetworkGraph;
 //! # use lightning::routing::router::{RouteParameters, find_route};
-//! # use lightning::routing::scoring::{Scorer, ScoringParameters};
+//! # use lightning::routing::scoring::{ProbabilisticScorer, ProbabilisticScoringParameters, 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, params: RouteParameters, network_graph: NetworkGraph) {
+//! # fn find_scored_route(payer: PublicKey, route_params: RouteParameters, network_graph: NetworkGraph) {
 //! # let logger = FakeLogger {};
 //! #
 //! // Use the default channel penalties.
-//! let scorer = Scorer::default();
+//! let params = ProbabilisticScoringParameters::default();
+//! let scorer = ProbabilisticScorer::new(params, &network_graph);
 //!
 //! // Or use custom channel penalties.
-//! let scorer = Scorer::new(ScoringParameters {
-//!     base_penalty_msat: 1000,
-//!     failure_penalty_msat: 2 * 1024 * 1000,
-//!     ..ScoringParameters::default()
-//! });
+//! let params = ProbabilisticScoringParameters {
+//!     liquidity_penalty_multiplier_msat: 2 * 1000,
+//!     ..ProbabilisticScoringParameters::default()
+//! };
+//! let scorer = ProbabilisticScorer::new(params, &network_graph);
 //!
-//! let route = find_route(&payer, &params, &network_graph, None, &logger, &scorer);
+//! let route = find_route(&payer, &route_params, &network_graph, None, &logger, &scorer);
 //! # }
 //! ```
 //!
 //! [`find_route`]: crate::routing::router::find_route
 
 use ln::msgs::DecodeError;
-use routing::network_graph::NodeId;
+use routing::network_graph::{NetworkGraph, NodeId};
 use routing::router::RouteHop;
-use util::ser::{Readable, Writeable, Writer};
+use util::ser::{Readable, ReadableArgs, Writeable, Writer};
 
 use prelude::*;
 use core::cell::{RefCell, RefMut};
-use core::ops::DerefMut;
+use core::ops::{Deref, DerefMut};
 use core::time::Duration;
 use io::{self, Read};
 use sync::{Mutex, MutexGuard};
@@ -82,16 +83,12 @@ pub trait Score $(: $supertrait)* {
        /// Returns the fee in msats willing to be paid to avoid routing `send_amt_msat` through the
        /// given channel in the direction from `source` to `target`.
        ///
-       /// The channel's capacity (less any other MPP parts which are also being considered for use in
-       /// the same payment) is given by `channel_capacity_msat`. It may be guessed from various
-       /// sources or assumed from no data at all.
-       ///
-       /// For hints provided in the invoice, we assume the channel has sufficient capacity to accept
-       /// the invoice's full amount, and provide a `channel_capacity_msat` of `None`. In all other
-       /// cases it is set to `Some`, even if we're guessing at the channel value.
-       ///
-       /// Your code should be overflow-safe through a `channel_capacity_msat` of 21 million BTC.
-       fn channel_penalty_msat(&self, short_channel_id: u64, send_amt_msat: u64, channel_capacity_msat: Option<u64>, source: &NodeId, target: &NodeId) -> u64;
+       /// The channel's capacity (less any other MPP parts that are also being considered for use in
+       /// the same payment) is given by `capacity_msat`. It may be determined from various sources
+       /// such as a chain data, network gossip, or invoice hints. For invoice hints, a capacity near
+       /// [`u64::max_value`] is given to indicate sufficient capacity for the invoice's full amount.
+       /// Thus, implementations should be overflow-safe.
+       fn channel_penalty_msat(&self, short_channel_id: u64, send_amt_msat: u64, capacity_msat: u64, source: &NodeId, target: &NodeId) -> u64;
 
        /// Handles updating channel penalties after failing to route through a channel.
        fn payment_path_failed(&mut self, path: &[&RouteHop], short_channel_id: u64);
@@ -101,8 +98,8 @@ pub trait Score $(: $supertrait)* {
 }
 
 impl<S: Score, T: DerefMut<Target=S> $(+ $supertrait)*> Score for T {
-       fn channel_penalty_msat(&self, short_channel_id: u64, send_amt_msat: u64, channel_capacity_msat: Option<u64>, source: &NodeId, target: &NodeId) -> u64 {
-               self.deref().channel_penalty_msat(short_channel_id, send_amt_msat, channel_capacity_msat, source, target)
+       fn channel_penalty_msat(&self, short_channel_id: u64, send_amt_msat: u64, capacity_msat: u64, source: &NodeId, target: &NodeId) -> u64 {
+               self.deref().channel_penalty_msat(short_channel_id, send_amt_msat, capacity_msat, source, target)
        }
 
        fn payment_path_failed(&mut self, path: &[&RouteHop], short_channel_id: u64) {
@@ -192,26 +189,55 @@ impl<'a, S: Writeable> Writeable for MutexGuard<'a, S> {
        }
 }
 
+/// [`Score`] implementation that uses a fixed penalty.
+pub struct FixedPenaltyScorer {
+       penalty_msat: u64,
+}
+
+impl_writeable_tlv_based!(FixedPenaltyScorer, {
+       (0, penalty_msat, required),
+});
+
+impl FixedPenaltyScorer {
+       /// Creates a new scorer using `penalty_msat`.
+       pub fn with_penalty(penalty_msat: u64) -> Self {
+               Self { penalty_msat }
+       }
+}
+
+impl Score for FixedPenaltyScorer {
+       fn channel_penalty_msat(&self, _: u64, _: u64, _: u64, _: &NodeId, _: &NodeId) -> u64 {
+               self.penalty_msat
+       }
+
+       fn payment_path_failed(&mut self, _path: &[&RouteHop], _short_channel_id: u64) {}
+
+       fn payment_path_successful(&mut self, _path: &[&RouteHop]) {}
+}
+
 /// [`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. Will further penalize channels that fail to relay payments.
 ///
-/// See [module-level documentation] for usage.
-///
-/// [module-level documentation]: crate::routing::scoring
-#[cfg(not(feature = "no-std"))]
-pub type Scorer = ScorerUsingTime::<std::time::Instant>;
-/// [`Score`] implementation that provides reasonable default behavior.
+/// See [module-level documentation] for usage and [`ScoringParameters`] for customization.
 ///
-/// Used to apply a fixed penalty to each channel, thus avoiding long paths when shorter paths with
-/// slightly higher fees are available. Will further penalize channels that fail to relay payments.
+/// # Note
 ///
-/// See [module-level documentation] for usage and [`ScoringParameters`] for customization.
+/// Mixing the `no-std` feature between serialization and deserialization results in undefined
+/// behavior.
 ///
 /// [module-level documentation]: crate::routing::scoring
+#[deprecated(
+       since = "0.0.105",
+       note = "ProbabilisticScorer should be used instead of Scorer.",
+)]
+pub type Scorer = ScorerUsingTime::<ConfiguredTime>;
+
+#[cfg(not(feature = "no-std"))]
+type ConfiguredTime = std::time::Instant;
 #[cfg(feature = "no-std")]
-pub type Scorer = ScorerUsingTime::<time::Eternity>;
+type ConfiguredTime = time::Eternity;
 
 // Note that ideally we'd hide ScorerUsingTime from public view by sealing it as well, but rustdoc
 // doesn't handle this well - instead exposing a `Scorer` which has no trait implementation(s) or
@@ -219,14 +245,8 @@ pub type Scorer = ScorerUsingTime::<time::Eternity>;
 
 /// [`Score`] implementation.
 ///
-/// See [`Scorer`] for details.
-///
-/// # Note
-///
-/// Mixing the `no-std` feature between serialization and deserialization results in undefined
-/// behavior.
-///
 /// (C-not exported) generally all users should use the [`Scorer`] type alias.
+#[doc(hidden)]
 pub struct ScorerUsingTime<T: Time> {
        params: ScoringParameters,
        // TODO: Remove entries of closed channels.
@@ -272,6 +292,8 @@ pub struct ScoringParameters {
        ///
        /// Successfully routing through a channel will immediately cut the penalty in half as well.
        ///
+       /// Default value: 1 hour
+       ///
        /// # Note
        ///
        /// When built with the `no-std` feature, time will never elapse. Therefore, this penalty will
@@ -309,18 +331,6 @@ impl<T: Time> ScorerUsingTime<T> {
                        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),
-                       overuse_penalty_start_1024th: 1024,
-                       overuse_penalty_msat_per_1024th: 0,
-               })
-       }
 }
 
 impl<T: Time> ChannelFailure<T> {
@@ -369,23 +379,19 @@ impl Default for ScoringParameters {
 
 impl<T: Time> Score for ScorerUsingTime<T> {
        fn channel_penalty_msat(
-               &self, short_channel_id: u64, send_amt_msat: u64, chan_capacity_opt: Option<u64>, _source: &NodeId, _target: &NodeId
+               &self, short_channel_id: u64, send_amt_msat: u64, capacity_msat: 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));
 
                let mut penalty_msat = self.params.base_penalty_msat + failure_penalty_msat;
-
-               if let Some(chan_capacity_msat) = chan_capacity_opt {
-                       let send_1024ths = send_amt_msat.checked_mul(1024).unwrap_or(u64::max_value()) / chan_capacity_msat;
-
-                       if send_1024ths > self.params.overuse_penalty_start_1024th as u64 {
-                               penalty_msat = penalty_msat.checked_add(
-                                               (send_1024ths - self.params.overuse_penalty_start_1024th as u64)
-                                               .checked_mul(self.params.overuse_penalty_msat_per_1024th).unwrap_or(u64::max_value()))
-                                       .unwrap_or(u64::max_value());
-                       }
+               let send_1024ths = send_amt_msat.checked_mul(1024).unwrap_or(u64::max_value()) / capacity_msat;
+               if send_1024ths > self.params.overuse_penalty_start_1024th as u64 {
+                       penalty_msat = penalty_msat.checked_add(
+                                       (send_1024ths - self.params.overuse_penalty_start_1024th as u64)
+                                       .checked_mul(self.params.overuse_penalty_msat_per_1024th).unwrap_or(u64::max_value()))
+                               .unwrap_or(u64::max_value());
                }
 
                penalty_msat
@@ -460,17 +466,418 @@ impl<T: Time> Readable for ChannelFailure<T> {
        }
 }
 
+/// [`Score`] implementation using channel success probability distributions.
+///
+/// Based on *Optimally Reliable & Cheap Payment Flows on the Lightning Network* by Rene Pickhardt
+/// and Stefan Richter [[1]]. Given the uncertainty of channel liquidity balances, probability
+/// distributions are defined based on knowledge learned from successful and unsuccessful attempts.
+/// Then the negative `log10` of the success probability is used to determine the cost of routing a
+/// specific HTLC amount through a channel.
+///
+/// Knowledge about channel liquidity balances takes the form of upper and lower bounds on the
+/// possible liquidity. Certainty of the bounds is decreased over time using a decay function. See
+/// [`ProbabilisticScoringParameters`] for details.
+///
+/// Since the scorer aims to learn the current channel liquidity balances, it works best for nodes
+/// with high payment volume or that actively probe the [`NetworkGraph`]. Nodes with low payment
+/// volume are more likely to experience failed payment paths, which would need to be retried.
+///
+/// # Note
+///
+/// Mixing the `no-std` feature between serialization and deserialization results in undefined
+/// behavior.
+///
+/// [1]: https://arxiv.org/abs/2107.05322
+pub type ProbabilisticScorer<G> = ProbabilisticScorerUsingTime::<G, ConfiguredTime>;
+
+/// Probabilistic [`Score`] implementation.
+///
+/// (C-not exported) generally all users should use the [`ProbabilisticScorer`] type alias.
+#[doc(hidden)]
+pub struct ProbabilisticScorerUsingTime<G: Deref<Target = NetworkGraph>, T: Time> {
+       params: ProbabilisticScoringParameters,
+       network_graph: G,
+       // TODO: Remove entries of closed channels.
+       channel_liquidities: HashMap<u64, ChannelLiquidity<T>>,
+}
+
+/// Parameters for configuring [`ProbabilisticScorer`].
+#[derive(Clone, Copy)]
+pub struct ProbabilisticScoringParameters {
+       /// A multiplier used to determine the amount in msats willing to be paid to avoid routing
+       /// through a channel, as per multiplying by the negative `log10` of the channel's success
+       /// probability for a payment.
+       ///
+       /// The success probability is determined by the effective channel capacity, the payment amount,
+       /// and knowledge learned from prior successful and unsuccessful payments. The lower bound of
+       /// the success probability is 0.01, effectively limiting the penalty to the range
+       /// `0..=2*liquidity_penalty_multiplier_msat`. The knowledge learned is decayed over time based
+       /// on [`liquidity_offset_half_life`].
+       ///
+       /// Default value: 10,000 msat
+       ///
+       /// [`liquidity_offset_half_life`]: Self::liquidity_offset_half_life
+       pub liquidity_penalty_multiplier_msat: u64,
+
+       /// The time required to elapse before any knowledge learned about channel liquidity balances is
+       /// cut in half.
+       ///
+       /// The bounds are defined in terms of offsets and are initially zero. Increasing the offsets
+       /// gives tighter bounds on the channel liquidity balance. Thus, halving the offsets decreases
+       /// the certainty of the channel liquidity balance.
+       ///
+       /// Default value: 1 hour
+       ///
+       /// # Note
+       ///
+       /// When built with the `no-std` feature, time will never elapse. Therefore, the channel
+       /// liquidity knowledge will never decay except when the bounds cross.
+       pub liquidity_offset_half_life: Duration,
+}
+
+impl_writeable_tlv_based!(ProbabilisticScoringParameters, {
+       (0, liquidity_penalty_multiplier_msat, required),
+       (2, liquidity_offset_half_life, required),
+});
+
+/// Accounting for channel liquidity balance uncertainty.
+///
+/// Direction is defined in terms of [`NodeId`] partial ordering, where the source node is the
+/// first node in the ordering of the channel's counterparties. Thus, swapping the two liquidity
+/// offset fields gives the opposite direction.
+struct ChannelLiquidity<T: Time> {
+       /// Lower channel liquidity bound in terms of an offset from zero.
+       min_liquidity_offset_msat: u64,
+
+       /// Upper channel liquidity bound in terms of an offset from the effective capacity.
+       max_liquidity_offset_msat: u64,
+
+       /// Time when the liquidity bounds were last modified.
+       last_updated: T,
+}
+
+/// A snapshot of [`ChannelLiquidity`] in one direction assuming a certain channel capacity and
+/// decayed with a given half life.
+struct DirectedChannelLiquidity<L: Deref<Target = u64>, T: Time, U: Deref<Target = T>> {
+       min_liquidity_offset_msat: L,
+       max_liquidity_offset_msat: L,
+       capacity_msat: u64,
+       last_updated: U,
+       now: T,
+       half_life: Duration,
+}
+
+impl<G: Deref<Target = NetworkGraph>, T: Time> ProbabilisticScorerUsingTime<G, T> {
+       /// Creates a new scorer using the given scoring parameters for sending payments from a node
+       /// through a network graph.
+       pub fn new(params: ProbabilisticScoringParameters, network_graph: G) -> Self {
+               Self {
+                       params,
+                       network_graph,
+                       channel_liquidities: HashMap::new(),
+               }
+       }
+
+       #[cfg(test)]
+       fn with_channel(mut self, short_channel_id: u64, liquidity: ChannelLiquidity<T>) -> Self {
+               assert!(self.channel_liquidities.insert(short_channel_id, liquidity).is_none());
+               self
+       }
+}
+
+impl Default for ProbabilisticScoringParameters {
+       fn default() -> Self {
+               Self {
+                       liquidity_penalty_multiplier_msat: 10_000,
+                       liquidity_offset_half_life: Duration::from_secs(3600),
+               }
+       }
+}
+
+impl<T: Time> ChannelLiquidity<T> {
+       #[inline]
+       fn new() -> Self {
+               Self {
+                       min_liquidity_offset_msat: 0,
+                       max_liquidity_offset_msat: 0,
+                       last_updated: T::now(),
+               }
+       }
+
+       /// Returns a view of the channel liquidity directed from `source` to `target` assuming
+       /// `capacity_msat`.
+       fn as_directed(
+               &self, source: &NodeId, target: &NodeId, capacity_msat: u64, half_life: Duration
+       ) -> DirectedChannelLiquidity<&u64, T, &T> {
+               let (min_liquidity_offset_msat, max_liquidity_offset_msat) = if source < target {
+                       (&self.min_liquidity_offset_msat, &self.max_liquidity_offset_msat)
+               } else {
+                       (&self.max_liquidity_offset_msat, &self.min_liquidity_offset_msat)
+               };
+
+               DirectedChannelLiquidity {
+                       min_liquidity_offset_msat,
+                       max_liquidity_offset_msat,
+                       capacity_msat,
+                       last_updated: &self.last_updated,
+                       now: T::now(),
+                       half_life,
+               }
+       }
+
+       /// Returns a mutable view of the channel liquidity directed from `source` to `target` assuming
+       /// `capacity_msat`.
+       fn as_directed_mut(
+               &mut self, source: &NodeId, target: &NodeId, capacity_msat: u64, half_life: Duration
+       ) -> DirectedChannelLiquidity<&mut u64, T, &mut T> {
+               let (min_liquidity_offset_msat, max_liquidity_offset_msat) = if source < target {
+                       (&mut self.min_liquidity_offset_msat, &mut self.max_liquidity_offset_msat)
+               } else {
+                       (&mut self.max_liquidity_offset_msat, &mut self.min_liquidity_offset_msat)
+               };
+
+               DirectedChannelLiquidity {
+                       min_liquidity_offset_msat,
+                       max_liquidity_offset_msat,
+                       capacity_msat,
+                       last_updated: &mut self.last_updated,
+                       now: T::now(),
+                       half_life,
+               }
+       }
+}
+
+impl<L: Deref<Target = u64>, T: Time, U: Deref<Target = T>> DirectedChannelLiquidity<L, T, U> {
+       /// Returns the success probability of routing the given HTLC `amount_msat` through the channel
+       /// in this direction.
+       fn success_probability(&self, amount_msat: u64) -> f64 {
+               let max_liquidity_msat = self.max_liquidity_msat();
+               let min_liquidity_msat = core::cmp::min(self.min_liquidity_msat(), max_liquidity_msat);
+               if amount_msat > max_liquidity_msat {
+                       0.0
+               } else if amount_msat <= min_liquidity_msat {
+                       1.0
+               } else {
+                       let numerator = max_liquidity_msat + 1 - amount_msat;
+                       let denominator = max_liquidity_msat + 1 - min_liquidity_msat;
+                       numerator as f64 / denominator as f64
+               }.max(0.01) // Lower bound the success probability to ensure some channel is selected.
+       }
+
+       /// Returns the lower bound of the channel liquidity balance in this direction.
+       fn min_liquidity_msat(&self) -> u64 {
+               self.decayed_offset_msat(*self.min_liquidity_offset_msat)
+       }
+
+       /// Returns the upper bound of the channel liquidity balance in this direction.
+       fn max_liquidity_msat(&self) -> u64 {
+               self.capacity_msat
+                       .checked_sub(self.decayed_offset_msat(*self.max_liquidity_offset_msat))
+                       .unwrap_or(0)
+       }
+
+       fn decayed_offset_msat(&self, offset_msat: u64) -> u64 {
+               self.now.duration_since(*self.last_updated).as_secs()
+                       .checked_div(self.half_life.as_secs())
+                       .and_then(|decays| offset_msat.checked_shr(decays as u32))
+                       .unwrap_or(0)
+       }
+}
+
+impl<L: DerefMut<Target = u64>, T: Time, U: DerefMut<Target = T>> DirectedChannelLiquidity<L, T, U> {
+       /// Adjusts the channel liquidity balance bounds when failing to route `amount_msat`.
+       fn failed_at_channel(&mut self, amount_msat: u64) {
+               if amount_msat < self.max_liquidity_msat() {
+                       self.set_max_liquidity_msat(amount_msat);
+               }
+       }
+
+       /// Adjusts the channel liquidity balance bounds when failing to route `amount_msat` downstream.
+       fn failed_downstream(&mut self, amount_msat: u64) {
+               if amount_msat > self.min_liquidity_msat() {
+                       self.set_min_liquidity_msat(amount_msat);
+               }
+       }
+
+       /// Adjusts the channel liquidity balance bounds when successfully routing `amount_msat`.
+       fn successful(&mut self, amount_msat: u64) {
+               let max_liquidity_msat = self.max_liquidity_msat().checked_sub(amount_msat).unwrap_or(0);
+               self.set_max_liquidity_msat(max_liquidity_msat);
+       }
+
+       /// Adjusts the lower bound of the channel liquidity balance in this direction.
+       fn set_min_liquidity_msat(&mut self, amount_msat: u64) {
+               *self.min_liquidity_offset_msat = amount_msat;
+               *self.max_liquidity_offset_msat = if amount_msat > self.max_liquidity_msat() {
+                       0
+               } else {
+                       self.decayed_offset_msat(*self.max_liquidity_offset_msat)
+               };
+               *self.last_updated = self.now;
+       }
+
+       /// Adjusts the upper bound of the channel liquidity balance in this direction.
+       fn set_max_liquidity_msat(&mut self, amount_msat: u64) {
+               *self.max_liquidity_offset_msat = self.capacity_msat.checked_sub(amount_msat).unwrap_or(0);
+               *self.min_liquidity_offset_msat = if amount_msat < self.min_liquidity_msat() {
+                       0
+               } else {
+                       self.decayed_offset_msat(*self.min_liquidity_offset_msat)
+               };
+               *self.last_updated = self.now;
+       }
+}
+
+impl<G: Deref<Target = NetworkGraph>, T: Time> Score for ProbabilisticScorerUsingTime<G, T> {
+       fn channel_penalty_msat(
+               &self, short_channel_id: u64, amount_msat: u64, capacity_msat: u64, source: &NodeId,
+               target: &NodeId
+       ) -> u64 {
+               let liquidity_penalty_multiplier_msat = self.params.liquidity_penalty_multiplier_msat;
+               let liquidity_offset_half_life = self.params.liquidity_offset_half_life;
+               let success_probability = self.channel_liquidities
+                       .get(&short_channel_id)
+                       .unwrap_or(&ChannelLiquidity::new())
+                       .as_directed(source, target, capacity_msat, liquidity_offset_half_life)
+                       .success_probability(amount_msat);
+               // NOTE: If success_probability is ever changed to return 0.0, log10 is undefined so return
+               // u64::max_value instead.
+               debug_assert!(success_probability > core::f64::EPSILON);
+               (-(success_probability.log10()) * liquidity_penalty_multiplier_msat as f64) as u64
+       }
+
+       fn payment_path_failed(&mut self, path: &[&RouteHop], short_channel_id: u64) {
+               let amount_msat = path.split_last().map(|(hop, _)| hop.fee_msat).unwrap_or(0);
+               let liquidity_offset_half_life = self.params.liquidity_offset_half_life;
+               let network_graph = self.network_graph.read_only();
+               for hop in path {
+                       let target = NodeId::from_pubkey(&hop.pubkey);
+                       let channel_directed_from_source = network_graph.channels()
+                               .get(&hop.short_channel_id)
+                               .and_then(|channel| channel.as_directed_to(&target));
+
+                       // Only score announced channels.
+                       if let Some((channel, source)) = channel_directed_from_source {
+                               let capacity_msat = channel.effective_capacity().as_msat();
+                               if hop.short_channel_id == short_channel_id {
+                                       self.channel_liquidities
+                                               .entry(hop.short_channel_id)
+                                               .or_insert_with(ChannelLiquidity::new)
+                                               .as_directed_mut(source, &target, capacity_msat, liquidity_offset_half_life)
+                                               .failed_at_channel(amount_msat);
+                                       break;
+                               }
+
+                               self.channel_liquidities
+                                       .entry(hop.short_channel_id)
+                                       .or_insert_with(ChannelLiquidity::new)
+                                       .as_directed_mut(source, &target, capacity_msat, liquidity_offset_half_life)
+                                       .failed_downstream(amount_msat);
+                       }
+               }
+       }
+
+       fn payment_path_successful(&mut self, path: &[&RouteHop]) {
+               let amount_msat = path.split_last().map(|(hop, _)| hop.fee_msat).unwrap_or(0);
+               let liquidity_offset_half_life = self.params.liquidity_offset_half_life;
+               let network_graph = self.network_graph.read_only();
+               for hop in path {
+                       let target = NodeId::from_pubkey(&hop.pubkey);
+                       let channel_directed_from_source = network_graph.channels()
+                               .get(&hop.short_channel_id)
+                               .and_then(|channel| channel.as_directed_to(&target));
+
+                       // Only score announced channels.
+                       if let Some((channel, source)) = channel_directed_from_source {
+                               let capacity_msat = channel.effective_capacity().as_msat();
+                               self.channel_liquidities
+                                       .entry(hop.short_channel_id)
+                                       .or_insert_with(ChannelLiquidity::new)
+                                       .as_directed_mut(source, &target, capacity_msat, liquidity_offset_half_life)
+                                       .successful(amount_msat);
+                       }
+               }
+       }
+}
+
+impl<G: Deref<Target = NetworkGraph>, T: Time> Writeable for ProbabilisticScorerUsingTime<G, T> {
+       #[inline]
+       fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+               write_tlv_fields!(w, {
+                       (0, self.channel_liquidities, required)
+               });
+               Ok(())
+       }
+}
+
+impl<G, T> ReadableArgs<(ProbabilisticScoringParameters, G)> for ProbabilisticScorerUsingTime<G, T>
+where
+       G: Deref<Target = NetworkGraph>,
+       T: Time,
+{
+       #[inline]
+       fn read<R: Read>(
+               r: &mut R, args: (ProbabilisticScoringParameters, G)
+       ) -> Result<Self, DecodeError> {
+               let (params, network_graph) = args;
+               let mut channel_liquidities = HashMap::new();
+               read_tlv_fields!(r, {
+                       (0, channel_liquidities, required)
+               });
+               Ok(Self {
+                       params,
+                       network_graph,
+                       channel_liquidities,
+               })
+       }
+}
+
+impl<T: Time> Writeable for ChannelLiquidity<T> {
+       #[inline]
+       fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+               let duration_since_epoch = T::duration_since_epoch() - self.last_updated.elapsed();
+               write_tlv_fields!(w, {
+                       (0, self.min_liquidity_offset_msat, required),
+                       (2, self.max_liquidity_offset_msat, required),
+                       (4, duration_since_epoch, required),
+               });
+               Ok(())
+       }
+}
+
+impl<T: Time> Readable for ChannelLiquidity<T> {
+       #[inline]
+       fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
+               let mut min_liquidity_offset_msat = 0;
+               let mut max_liquidity_offset_msat = 0;
+               let mut duration_since_epoch = Duration::from_secs(0);
+               read_tlv_fields!(r, {
+                       (0, min_liquidity_offset_msat, required),
+                       (2, max_liquidity_offset_msat, required),
+                       (4, duration_since_epoch, required),
+               });
+               Ok(Self {
+                       min_liquidity_offset_msat,
+                       max_liquidity_offset_msat,
+                       last_updated: T::now() - (T::duration_since_epoch() - duration_since_epoch),
+               })
+       }
+}
+
 pub(crate) mod time {
        use core::ops::Sub;
        use core::time::Duration;
        /// A measurement of time.
-       pub trait Time: Sub<Duration, Output = Self> where Self: Sized {
+       pub trait Time: Copy + 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 between `earlier` and `self`.
+               fn duration_since(&self, earlier: Self) -> Duration;
+
                /// Returns the amount of time passed since the beginning of [`Time`].
                ///
                /// Used during (de-)serialization.
@@ -478,7 +885,7 @@ pub(crate) mod time {
        }
 
        /// A state in which time has no meaning.
-       #[derive(Debug, PartialEq, Eq)]
+       #[derive(Clone, Copy, Debug, PartialEq, Eq)]
        pub struct Eternity;
 
        #[cfg(not(feature = "no-std"))]
@@ -487,6 +894,10 @@ pub(crate) mod time {
                        std::time::Instant::now()
                }
 
+               fn duration_since(&self, earlier: Self) -> Duration {
+                       self.duration_since(earlier)
+               }
+
                fn duration_since_epoch() -> Duration {
                        use std::time::SystemTime;
                        SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap()
@@ -502,6 +913,10 @@ pub(crate) mod time {
                        Self
                }
 
+               fn duration_since(&self, _earlier: Self) -> Duration {
+                       Duration::from_secs(0)
+               }
+
                fn duration_since_epoch() -> Duration {
                        Duration::from_secs(0)
                }
@@ -524,23 +939,30 @@ pub(crate) use self::time::Time;
 
 #[cfg(test)]
 mod tests {
-       use super::{ScoringParameters, ScorerUsingTime, Time};
+       use super::{ChannelLiquidity, ProbabilisticScoringParameters, ProbabilisticScorerUsingTime, ScoringParameters, ScorerUsingTime, Time};
        use super::time::Eternity;
 
        use ln::features::{ChannelFeatures, NodeFeatures};
+       use ln::msgs::{ChannelAnnouncement, ChannelUpdate, OptionalField, UnsignedChannelAnnouncement, UnsignedChannelUpdate};
        use routing::scoring::Score;
-       use routing::network_graph::NodeId;
+       use routing::network_graph::{NetworkGraph, NodeId};
        use routing::router::RouteHop;
-       use util::ser::{Readable, Writeable};
+       use util::ser::{Readable, ReadableArgs, Writeable};
 
-       use bitcoin::secp256k1::PublicKey;
+       use bitcoin::blockdata::constants::genesis_block;
+       use bitcoin::hashes::Hash;
+       use bitcoin::hashes::sha256d::Hash as Sha256dHash;
+       use bitcoin::network::constants::Network;
+       use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
        use core::cell::Cell;
        use core::ops::Sub;
        use core::time::Duration;
        use io;
 
+       // `Time` tests
+
        /// Time that can be advanced manually in tests.
-       #[derive(Debug, PartialEq, Eq)]
+       #[derive(Clone, Copy, Debug, PartialEq, Eq)]
        struct SinceEpoch(Duration);
 
        impl SinceEpoch {
@@ -558,6 +980,10 @@ mod tests {
                        Self(Self::duration_since_epoch())
                }
 
+               fn duration_since(&self, earlier: Self) -> Duration {
+                       self.0 - earlier.0
+               }
+
                fn duration_since_epoch() -> Duration {
                        Self::ELAPSED.with(|elapsed| elapsed.get())
                }
@@ -600,15 +1026,35 @@ mod tests {
                assert_eq!(later - elapsed, now);
        }
 
+       // `Scorer` tests
+
        /// A scorer for testing with time that can be manually advanced.
        type Scorer = ScorerUsingTime::<SinceEpoch>;
 
+       fn source_privkey() -> SecretKey {
+               SecretKey::from_slice(&[42; 32]).unwrap()
+       }
+
+       fn target_privkey() -> SecretKey {
+               SecretKey::from_slice(&[43; 32]).unwrap()
+       }
+
+       fn source_pubkey() -> PublicKey {
+               let secp_ctx = Secp256k1::new();
+               PublicKey::from_secret_key(&secp_ctx, &source_privkey())
+       }
+
+       fn target_pubkey() -> PublicKey {
+               let secp_ctx = Secp256k1::new();
+               PublicKey::from_secret_key(&secp_ctx, &target_privkey())
+       }
+
        fn source_node_id() -> NodeId {
-               NodeId::from_pubkey(&PublicKey::from_slice(&hex::decode("02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619").unwrap()[..]).unwrap())
+               NodeId::from_pubkey(&source_pubkey())
        }
 
        fn target_node_id() -> NodeId {
-               NodeId::from_pubkey(&PublicKey::from_slice(&hex::decode("0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c").unwrap()[..]).unwrap())
+               NodeId::from_pubkey(&target_pubkey())
        }
 
        #[test]
@@ -622,10 +1068,10 @@ mod tests {
                });
                let source = source_node_id();
                let target = target_node_id();
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
 
                SinceEpoch::advance(Duration::from_secs(1));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
        }
 
        #[test]
@@ -639,16 +1085,16 @@ mod tests {
                });
                let source = source_node_id();
                let target = target_node_id();
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_064);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_064);
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_128);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_128);
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_192);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_192);
        }
 
        #[test]
@@ -662,25 +1108,25 @@ mod tests {
                });
                let source = source_node_id();
                let target = target_node_id();
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);
 
                SinceEpoch::advance(Duration::from_secs(9));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);
 
                SinceEpoch::advance(Duration::from_secs(1));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_256);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);
 
                SinceEpoch::advance(Duration::from_secs(10 * 8));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_001);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_001);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
        }
 
        #[test]
@@ -694,18 +1140,18 @@ mod tests {
                });
                let source = source_node_id();
                let target = target_node_id();
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);
 
                // An unchecked right shift 64 bits or more in ChannelFailure::decayed_penalty_msat would
                // cause an overflow.
                SinceEpoch::advance(Duration::from_secs(10 * 64));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
        }
 
        #[test]
@@ -719,19 +1165,19 @@ mod tests {
                });
                let source = source_node_id();
                let target = target_node_id();
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_256);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_768);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_768);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_384);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_384);
        }
 
        #[test]
@@ -745,13 +1191,13 @@ mod tests {
                });
                let source = source_node_id();
                let target = target_node_id();
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_256);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);
 
                let hop = RouteHop {
                        pubkey: PublicKey::from_slice(target.as_slice()).unwrap(),
@@ -762,10 +1208,10 @@ mod tests {
                        cltv_expiry_delta: 18,
                };
                scorer.payment_path_successful(&[&hop]);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_128);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_128);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_064);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_064);
        }
 
        #[test]
@@ -781,20 +1227,20 @@ mod tests {
                let target = target_node_id();
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_256);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);
 
                scorer.payment_path_failed(&[], 43);
-               assert_eq!(scorer.channel_penalty_msat(43, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(scorer.channel_penalty_msat(43, 1, 1, &source, &target), 1_512);
 
                let mut serialized_scorer = Vec::new();
                scorer.write(&mut serialized_scorer).unwrap();
 
                let deserialized_scorer = <Scorer>::read(&mut io::Cursor::new(&serialized_scorer)).unwrap();
-               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_256);
-               assert_eq!(deserialized_scorer.channel_penalty_msat(43, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);
+               assert_eq!(deserialized_scorer.channel_penalty_msat(43, 1, 1, &source, &target), 1_512);
        }
 
        #[test]
@@ -810,7 +1256,7 @@ mod tests {
                let target = target_node_id();
 
                scorer.payment_path_failed(&[], 42);
-               assert_eq!(scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_512);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);
 
                let mut serialized_scorer = Vec::new();
                scorer.write(&mut serialized_scorer).unwrap();
@@ -818,10 +1264,10 @@ mod tests {
                SinceEpoch::advance(Duration::from_secs(10));
 
                let deserialized_scorer = <Scorer>::read(&mut io::Cursor::new(&serialized_scorer)).unwrap();
-               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_256);
+               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);
 
                SinceEpoch::advance(Duration::from_secs(10));
-               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, Some(1), &source, &target), 1_128);
+               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_128);
        }
 
        #[test]
@@ -836,11 +1282,631 @@ mod tests {
                let source = source_node_id();
                let target = target_node_id();
 
-               assert_eq!(scorer.channel_penalty_msat(42, 1_000, None, &source, &target), 0);
-               assert_eq!(scorer.channel_penalty_msat(42, 1_000, Some(1_024_000), &source, &target), 0);
-               assert_eq!(scorer.channel_penalty_msat(42, 256_999, Some(1_024_000), &source, &target), 0);
-               assert_eq!(scorer.channel_penalty_msat(42, 257_000, Some(1_024_000), &source, &target), 100);
-               assert_eq!(scorer.channel_penalty_msat(42, 258_000, Some(1_024_000), &source, &target), 200);
-               assert_eq!(scorer.channel_penalty_msat(42, 512_000, Some(1_024_000), &source, &target), 256 * 100);
+               assert_eq!(scorer.channel_penalty_msat(42, 1_000, 1_024_000, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 256_999, 1_024_000, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 257_000, 1_024_000, &source, &target), 100);
+               assert_eq!(scorer.channel_penalty_msat(42, 258_000, 1_024_000, &source, &target), 200);
+               assert_eq!(scorer.channel_penalty_msat(42, 512_000, 1_024_000, &source, &target), 256 * 100);
+       }
+
+       // `ProbabilisticScorer` tests
+
+       /// A probabilistic scorer for testing with time that can be manually advanced.
+       type ProbabilisticScorer<'a> = ProbabilisticScorerUsingTime::<&'a NetworkGraph, SinceEpoch>;
+
+       fn sender_privkey() -> SecretKey {
+               SecretKey::from_slice(&[41; 32]).unwrap()
+       }
+
+       fn recipient_privkey() -> SecretKey {
+               SecretKey::from_slice(&[45; 32]).unwrap()
+       }
+
+       fn sender_pubkey() -> PublicKey {
+               let secp_ctx = Secp256k1::new();
+               PublicKey::from_secret_key(&secp_ctx, &sender_privkey())
+       }
+
+       fn recipient_pubkey() -> PublicKey {
+               let secp_ctx = Secp256k1::new();
+               PublicKey::from_secret_key(&secp_ctx, &recipient_privkey())
+       }
+
+       fn sender_node_id() -> NodeId {
+               NodeId::from_pubkey(&sender_pubkey())
+       }
+
+       fn recipient_node_id() -> NodeId {
+               NodeId::from_pubkey(&recipient_pubkey())
+       }
+
+       fn network_graph() -> NetworkGraph {
+               let genesis_hash = genesis_block(Network::Testnet).header.block_hash();
+               let mut network_graph = NetworkGraph::new(genesis_hash);
+               add_channel(&mut network_graph, 42, source_privkey(), target_privkey());
+               add_channel(&mut network_graph, 43, target_privkey(), recipient_privkey());
+
+               network_graph
+       }
+
+       fn add_channel(
+               network_graph: &mut NetworkGraph, short_channel_id: u64, node_1_key: SecretKey,
+               node_2_key: SecretKey
+       ) {
+               let genesis_hash = genesis_block(Network::Testnet).header.block_hash();
+               let node_1_secret = &SecretKey::from_slice(&[39; 32]).unwrap();
+               let node_2_secret = &SecretKey::from_slice(&[40; 32]).unwrap();
+               let secp_ctx = Secp256k1::new();
+               let unsigned_announcement = UnsignedChannelAnnouncement {
+                       features: ChannelFeatures::known(),
+                       chain_hash: genesis_hash,
+                       short_channel_id,
+                       node_id_1: PublicKey::from_secret_key(&secp_ctx, &node_1_key),
+                       node_id_2: PublicKey::from_secret_key(&secp_ctx, &node_2_key),
+                       bitcoin_key_1: PublicKey::from_secret_key(&secp_ctx, &node_1_secret),
+                       bitcoin_key_2: PublicKey::from_secret_key(&secp_ctx, &node_2_secret),
+                       excess_data: Vec::new(),
+               };
+               let msghash = hash_to_message!(&Sha256dHash::hash(&unsigned_announcement.encode()[..])[..]);
+               let signed_announcement = ChannelAnnouncement {
+                       node_signature_1: secp_ctx.sign(&msghash, &node_1_key),
+                       node_signature_2: secp_ctx.sign(&msghash, &node_2_key),
+                       bitcoin_signature_1: secp_ctx.sign(&msghash, &node_1_secret),
+                       bitcoin_signature_2: secp_ctx.sign(&msghash, &node_2_secret),
+                       contents: unsigned_announcement,
+               };
+               let chain_source: Option<&::util::test_utils::TestChainSource> = None;
+               network_graph.update_channel_from_announcement(
+                       &signed_announcement, &chain_source, &secp_ctx).unwrap();
+               update_channel(network_graph, short_channel_id, node_1_key, 0);
+               update_channel(network_graph, short_channel_id, node_2_key, 1);
+       }
+
+       fn update_channel(
+               network_graph: &mut NetworkGraph, short_channel_id: u64, node_key: SecretKey, flags: u8
+       ) {
+               let genesis_hash = genesis_block(Network::Testnet).header.block_hash();
+               let secp_ctx = Secp256k1::new();
+               let unsigned_update = UnsignedChannelUpdate {
+                       chain_hash: genesis_hash,
+                       short_channel_id,
+                       timestamp: 100,
+                       flags,
+                       cltv_expiry_delta: 18,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: OptionalField::Present(1_000),
+                       fee_base_msat: 1,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new(),
+               };
+               let msghash = hash_to_message!(&Sha256dHash::hash(&unsigned_update.encode()[..])[..]);
+               let signed_update = ChannelUpdate {
+                       signature: secp_ctx.sign(&msghash, &node_key),
+                       contents: unsigned_update,
+               };
+               network_graph.update_channel(&signed_update, &secp_ctx).unwrap();
+       }
+
+       fn payment_path_for_amount(amount_msat: u64) -> Vec<RouteHop> {
+               vec![
+                       RouteHop {
+                               pubkey: source_pubkey(),
+                               node_features: NodeFeatures::known(),
+                               short_channel_id: 41,
+                               channel_features: ChannelFeatures::known(),
+                               fee_msat: 1,
+                               cltv_expiry_delta: 18,
+                       },
+                       RouteHop {
+                               pubkey: target_pubkey(),
+                               node_features: NodeFeatures::known(),
+                               short_channel_id: 42,
+                               channel_features: ChannelFeatures::known(),
+                               fee_msat: 2,
+                               cltv_expiry_delta: 18,
+                       },
+                       RouteHop {
+                               pubkey: recipient_pubkey(),
+                               node_features: NodeFeatures::known(),
+                               short_channel_id: 43,
+                               channel_features: ChannelFeatures::known(),
+                               fee_msat: amount_msat,
+                               cltv_expiry_delta: 18,
+                       },
+               ]
+       }
+
+       #[test]
+       fn liquidity_bounds_directed_from_lowest_node_id() {
+               let last_updated = SinceEpoch::now();
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters::default();
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph)
+                       .with_channel(42,
+                               ChannelLiquidity {
+                                       min_liquidity_offset_msat: 700, max_liquidity_offset_msat: 100, last_updated
+                               })
+                       .with_channel(43,
+                               ChannelLiquidity {
+                                       min_liquidity_offset_msat: 700, max_liquidity_offset_msat: 100, last_updated
+                               });
+               let source = source_node_id();
+               let target = target_node_id();
+               let recipient = recipient_node_id();
+               assert!(source > target);
+               assert!(target < recipient);
+
+               // Update minimum liquidity.
+
+               let liquidity_offset_half_life = scorer.params.liquidity_offset_half_life;
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 100);
+               assert_eq!(liquidity.max_liquidity_msat(), 300);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 700);
+               assert_eq!(liquidity.max_liquidity_msat(), 900);
+
+               scorer.channel_liquidities.get_mut(&42).unwrap()
+                       .as_directed_mut(&source, &target, 1_000, liquidity_offset_half_life)
+                       .set_min_liquidity_msat(200);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 200);
+               assert_eq!(liquidity.max_liquidity_msat(), 300);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 700);
+               assert_eq!(liquidity.max_liquidity_msat(), 800);
+
+               // Update maximum liquidity.
+
+               let liquidity = scorer.channel_liquidities.get(&43).unwrap()
+                       .as_directed(&target, &recipient, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 700);
+               assert_eq!(liquidity.max_liquidity_msat(), 900);
+
+               let liquidity = scorer.channel_liquidities.get(&43).unwrap()
+                       .as_directed(&recipient, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 100);
+               assert_eq!(liquidity.max_liquidity_msat(), 300);
+
+               scorer.channel_liquidities.get_mut(&43).unwrap()
+                       .as_directed_mut(&target, &recipient, 1_000, liquidity_offset_half_life)
+                       .set_max_liquidity_msat(200);
+
+               let liquidity = scorer.channel_liquidities.get(&43).unwrap()
+                       .as_directed(&target, &recipient, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 0);
+               assert_eq!(liquidity.max_liquidity_msat(), 200);
+
+               let liquidity = scorer.channel_liquidities.get(&43).unwrap()
+                       .as_directed(&recipient, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 800);
+               assert_eq!(liquidity.max_liquidity_msat(), 1000);
+       }
+
+       #[test]
+       fn resets_liquidity_upper_bound_when_crossed_by_lower_bound() {
+               let last_updated = SinceEpoch::now();
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters::default();
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph)
+                       .with_channel(42,
+                               ChannelLiquidity {
+                                       min_liquidity_offset_msat: 200, max_liquidity_offset_msat: 400, last_updated
+                               });
+               let source = source_node_id();
+               let target = target_node_id();
+               assert!(source > target);
+
+               // Check initial bounds.
+               let liquidity_offset_half_life = scorer.params.liquidity_offset_half_life;
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 400);
+               assert_eq!(liquidity.max_liquidity_msat(), 800);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 200);
+               assert_eq!(liquidity.max_liquidity_msat(), 600);
+
+               // Reset from source to target.
+               scorer.channel_liquidities.get_mut(&42).unwrap()
+                       .as_directed_mut(&source, &target, 1_000, liquidity_offset_half_life)
+                       .set_min_liquidity_msat(900);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 900);
+               assert_eq!(liquidity.max_liquidity_msat(), 1_000);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 0);
+               assert_eq!(liquidity.max_liquidity_msat(), 100);
+
+               // Reset from target to source.
+               scorer.channel_liquidities.get_mut(&42).unwrap()
+                       .as_directed_mut(&target, &source, 1_000, liquidity_offset_half_life)
+                       .set_min_liquidity_msat(400);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 0);
+               assert_eq!(liquidity.max_liquidity_msat(), 600);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 400);
+               assert_eq!(liquidity.max_liquidity_msat(), 1_000);
+       }
+
+       #[test]
+       fn resets_liquidity_lower_bound_when_crossed_by_upper_bound() {
+               let last_updated = SinceEpoch::now();
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters::default();
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph)
+                       .with_channel(42,
+                               ChannelLiquidity {
+                                       min_liquidity_offset_msat: 200, max_liquidity_offset_msat: 400, last_updated
+                               });
+               let source = source_node_id();
+               let target = target_node_id();
+               assert!(source > target);
+
+               // Check initial bounds.
+               let liquidity_offset_half_life = scorer.params.liquidity_offset_half_life;
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 400);
+               assert_eq!(liquidity.max_liquidity_msat(), 800);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 200);
+               assert_eq!(liquidity.max_liquidity_msat(), 600);
+
+               // Reset from source to target.
+               scorer.channel_liquidities.get_mut(&42).unwrap()
+                       .as_directed_mut(&source, &target, 1_000, liquidity_offset_half_life)
+                       .set_max_liquidity_msat(300);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 0);
+               assert_eq!(liquidity.max_liquidity_msat(), 300);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 700);
+               assert_eq!(liquidity.max_liquidity_msat(), 1_000);
+
+               // Reset from target to source.
+               scorer.channel_liquidities.get_mut(&42).unwrap()
+                       .as_directed_mut(&target, &source, 1_000, liquidity_offset_half_life)
+                       .set_max_liquidity_msat(600);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 400);
+               assert_eq!(liquidity.max_liquidity_msat(), 1_000);
+
+               let liquidity = scorer.channel_liquidities.get(&42).unwrap()
+                       .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
+               assert_eq!(liquidity.min_liquidity_msat(), 0);
+               assert_eq!(liquidity.max_liquidity_msat(), 600);
+       }
+
+       #[test]
+       fn increased_penalty_nearing_liquidity_upper_bound() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000, ..Default::default()
+               };
+               let scorer = ProbabilisticScorer::new(params, &network_graph);
+               let source = source_node_id();
+               let target = target_node_id();
+
+               assert_eq!(scorer.channel_penalty_msat(42, 100, 100_000, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 1_000, 100_000, &source, &target), 4);
+               assert_eq!(scorer.channel_penalty_msat(42, 10_000, 100_000, &source, &target), 45);
+               assert_eq!(scorer.channel_penalty_msat(42, 100_000, 100_000, &source, &target), 2_000);
+
+               assert_eq!(scorer.channel_penalty_msat(42, 125, 1_000, &source, &target), 57);
+               assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 124);
+               assert_eq!(scorer.channel_penalty_msat(42, 375, 1_000, &source, &target), 203);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
+               assert_eq!(scorer.channel_penalty_msat(42, 625, 1_000, &source, &target), 425);
+               assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), 600);
+               assert_eq!(scorer.channel_penalty_msat(42, 875, 1_000, &source, &target), 900);
+       }
+
+       #[test]
+       fn constant_penalty_outside_liquidity_bounds() {
+               let last_updated = SinceEpoch::now();
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000, ..Default::default()
+               };
+               let scorer = ProbabilisticScorer::new(params, &network_graph)
+                       .with_channel(42,
+                               ChannelLiquidity {
+                                       min_liquidity_offset_msat: 40, max_liquidity_offset_msat: 40, last_updated
+                               });
+               let source = source_node_id();
+               let target = target_node_id();
+
+               assert_eq!(scorer.channel_penalty_msat(42, 39, 100, &source, &target), 0);
+               assert_ne!(scorer.channel_penalty_msat(42, 50, 100, &source, &target), 0);
+               assert_ne!(scorer.channel_penalty_msat(42, 50, 100, &source, &target), 2_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 61, 100, &source, &target), 2_000);
+       }
+
+       #[test]
+       fn does_not_further_penalize_own_channel() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000, ..Default::default()
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let sender = sender_node_id();
+               let source = source_node_id();
+               let failed_path = payment_path_for_amount(500);
+               let successful_path = payment_path_for_amount(200);
+
+               assert_eq!(scorer.channel_penalty_msat(41, 500, 1_000, &sender, &source), 300);
+
+               scorer.payment_path_failed(&failed_path.iter().collect::<Vec<_>>(), 41);
+               assert_eq!(scorer.channel_penalty_msat(41, 500, 1_000, &sender, &source), 300);
+
+               scorer.payment_path_successful(&successful_path.iter().collect::<Vec<_>>());
+               assert_eq!(scorer.channel_penalty_msat(41, 500, 1_000, &sender, &source), 300);
+       }
+
+       #[test]
+       fn sets_liquidity_lower_bound_on_downstream_failure() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000, ..Default::default()
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let source = source_node_id();
+               let target = target_node_id();
+               let path = payment_path_for_amount(500);
+
+               assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 124);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
+               assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), 600);
+
+               scorer.payment_path_failed(&path.iter().collect::<Vec<_>>(), 43);
+
+               assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), 300);
+       }
+
+       #[test]
+       fn sets_liquidity_upper_bound_on_failure() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000, ..Default::default()
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let source = source_node_id();
+               let target = target_node_id();
+               let path = payment_path_for_amount(500);
+
+               assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 124);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
+               assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), 600);
+
+               scorer.payment_path_failed(&path.iter().collect::<Vec<_>>(), 42);
+
+               assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 300);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 2_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), 2_000);
+       }
+
+       #[test]
+       fn reduces_liquidity_upper_bound_along_path_on_success() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000, ..Default::default()
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let sender = sender_node_id();
+               let source = source_node_id();
+               let target = target_node_id();
+               let recipient = recipient_node_id();
+               let path = payment_path_for_amount(500);
+
+               assert_eq!(scorer.channel_penalty_msat(41, 250, 1_000, &sender, &source), 124);
+               assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 124);
+               assert_eq!(scorer.channel_penalty_msat(43, 250, 1_000, &target, &recipient), 124);
+
+               scorer.payment_path_successful(&path.iter().collect::<Vec<_>>());
+
+               assert_eq!(scorer.channel_penalty_msat(41, 250, 1_000, &sender, &source), 124);
+               assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 300);
+               assert_eq!(scorer.channel_penalty_msat(43, 250, 1_000, &target, &recipient), 300);
+       }
+
+       #[test]
+       fn decays_liquidity_bounds_over_time() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000,
+                       liquidity_offset_half_life: Duration::from_secs(10),
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let source = source_node_id();
+               let target = target_node_id();
+
+               assert_eq!(scorer.channel_penalty_msat(42, 0, 1_024, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024, &source, &target), 2_000);
+
+               scorer.payment_path_failed(&payment_path_for_amount(768).iter().collect::<Vec<_>>(), 42);
+               scorer.payment_path_failed(&payment_path_for_amount(128).iter().collect::<Vec<_>>(), 43);
+
+               assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 92);
+               assert_eq!(scorer.channel_penalty_msat(42, 768, 1_024, &source, &target), 1_424);
+               assert_eq!(scorer.channel_penalty_msat(42, 896, 1_024, &source, &target), 2_000);
+
+               SinceEpoch::advance(Duration::from_secs(9));
+               assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 92);
+               assert_eq!(scorer.channel_penalty_msat(42, 768, 1_024, &source, &target), 1_424);
+               assert_eq!(scorer.channel_penalty_msat(42, 896, 1_024, &source, &target), 2_000);
+
+               SinceEpoch::advance(Duration::from_secs(1));
+               assert_eq!(scorer.channel_penalty_msat(42, 64, 1_024, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 34);
+               assert_eq!(scorer.channel_penalty_msat(42, 896, 1_024, &source, &target), 1_812);
+               assert_eq!(scorer.channel_penalty_msat(42, 960, 1_024, &source, &target), 2_000);
+
+               // Fully decay liquidity lower bound.
+               SinceEpoch::advance(Duration::from_secs(10 * 7));
+               assert_eq!(scorer.channel_penalty_msat(42, 0, 1_024, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 1, 1_024, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 1_023, 1_024, &source, &target), 2_000);
+               assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024, &source, &target), 2_000);
+
+               // Fully decay liquidity upper bound.
+               SinceEpoch::advance(Duration::from_secs(10));
+               assert_eq!(scorer.channel_penalty_msat(42, 0, 1_024, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024, &source, &target), 2_000);
+
+               SinceEpoch::advance(Duration::from_secs(10));
+               assert_eq!(scorer.channel_penalty_msat(42, 0, 1_024, &source, &target), 0);
+               assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024, &source, &target), 2_000);
+       }
+
+       #[test]
+       fn decays_liquidity_bounds_without_shift_overflow() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000,
+                       liquidity_offset_half_life: Duration::from_secs(10),
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let source = source_node_id();
+               let target = target_node_id();
+               assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 124);
+
+               scorer.payment_path_failed(&payment_path_for_amount(512).iter().collect::<Vec<_>>(), 42);
+               assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 281);
+
+               // An unchecked right shift 64 bits or more in DirectedChannelLiquidity::decayed_offset_msat
+               // would cause an overflow.
+               SinceEpoch::advance(Duration::from_secs(10 * 64));
+               assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 124);
+
+               SinceEpoch::advance(Duration::from_secs(10));
+               assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 124);
+       }
+
+       #[test]
+       fn restricts_liquidity_bounds_after_decay() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000,
+                       liquidity_offset_half_life: Duration::from_secs(10),
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let source = source_node_id();
+               let target = target_node_id();
+
+               assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 300);
+
+               // More knowledge gives higher confidence (256, 768), meaning a lower penalty.
+               scorer.payment_path_failed(&payment_path_for_amount(768).iter().collect::<Vec<_>>(), 42);
+               scorer.payment_path_failed(&payment_path_for_amount(256).iter().collect::<Vec<_>>(), 43);
+               assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 281);
+
+               // Decaying knowledge gives less confidence (128, 896), meaning a higher penalty.
+               SinceEpoch::advance(Duration::from_secs(10));
+               assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 293);
+
+               // Reducing the upper bound gives more confidence (128, 832) that the payment amount (512)
+               // is closer to the upper bound, meaning a higher penalty.
+               scorer.payment_path_successful(&payment_path_for_amount(64).iter().collect::<Vec<_>>());
+               assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 333);
+
+               // Increasing the lower bound gives more confidence (256, 832) that the payment amount (512)
+               // is closer to the lower bound, meaning a lower penalty.
+               scorer.payment_path_failed(&payment_path_for_amount(256).iter().collect::<Vec<_>>(), 43);
+               assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 247);
+
+               // Further decaying affects the lower bound more than the upper bound (128, 928).
+               SinceEpoch::advance(Duration::from_secs(10));
+               assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 280);
+       }
+
+       #[test]
+       fn restores_persisted_liquidity_bounds() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000,
+                       liquidity_offset_half_life: Duration::from_secs(10),
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let source = source_node_id();
+               let target = target_node_id();
+
+               scorer.payment_path_failed(&payment_path_for_amount(500).iter().collect::<Vec<_>>(), 42);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 2_000);
+
+               SinceEpoch::advance(Duration::from_secs(10));
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 475);
+
+               scorer.payment_path_failed(&payment_path_for_amount(250).iter().collect::<Vec<_>>(), 43);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
+
+               let mut serialized_scorer = Vec::new();
+               scorer.write(&mut serialized_scorer).unwrap();
+
+               let mut serialized_scorer = io::Cursor::new(&serialized_scorer);
+               let deserialized_scorer =
+                       <ProbabilisticScorer>::read(&mut serialized_scorer, (params, &network_graph)).unwrap();
+               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
+       }
+
+       #[test]
+       fn decays_persisted_liquidity_bounds() {
+               let network_graph = network_graph();
+               let params = ProbabilisticScoringParameters {
+                       liquidity_penalty_multiplier_msat: 1_000,
+                       liquidity_offset_half_life: Duration::from_secs(10),
+               };
+               let mut scorer = ProbabilisticScorer::new(params, &network_graph);
+               let source = source_node_id();
+               let target = target_node_id();
+
+               scorer.payment_path_failed(&payment_path_for_amount(500).iter().collect::<Vec<_>>(), 42);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 2_000);
+
+               let mut serialized_scorer = Vec::new();
+               scorer.write(&mut serialized_scorer).unwrap();
+
+               SinceEpoch::advance(Duration::from_secs(10));
+
+               let mut serialized_scorer = io::Cursor::new(&serialized_scorer);
+               let deserialized_scorer =
+                       <ProbabilisticScorer>::read(&mut serialized_scorer, (params, &network_graph)).unwrap();
+               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 475);
+
+               scorer.payment_path_failed(&payment_path_for_amount(250).iter().collect::<Vec<_>>(), 43);
+               assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
+
+               SinceEpoch::advance(Duration::from_secs(10));
+               assert_eq!(deserialized_scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 367);
        }
 }