_ Git - rust-lightning/blob - lightning/src/routing/scorer.rs

   1 // This file is Copyright its original authors, visible in version control
   2 // history.
   3 //
   4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
   5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
   7 // You may not use this file except in accordance with one or both of these
   8 // licenses.
   9
  10 //! Utilities for scoring payment channels.
  11 //!
  12 //! [`Scorer`] may be given to [`find_route`] to score payment channels during path finding when a
  13 //! custom [`routing::Score`] implementation is not needed.
  14 //!
  15 //! # Example
  16 //!
  17 //! ```
  18 //! # extern crate secp256k1;
  19 //! #
  20 //! # use lightning::routing::network_graph::NetworkGraph;
  21 //! # use lightning::routing::router::{RouteParameters, find_route};
  22 //! # use lightning::routing::scorer::{Scorer, ScoringParameters};
  23 //! # use lightning::util::logger::{Logger, Record};
  24 //! # use secp256k1::key::PublicKey;
  25 //! #
  26 //! # struct FakeLogger {};
  27 //! # impl Logger for FakeLogger {
  28 //! #     fn log(&self, record: &Record) { unimplemented!() }
  29 //! # }
  30 //! # fn find_scored_route(payer: PublicKey, params: RouteParameters, network_graph: NetworkGraph) {
  31 //! # let logger = FakeLogger {};
  32 //! #
  33 //! // Use the default channel penalties.
  34 //! let scorer = Scorer::default();
  35 //!
  36 //! // Or use custom channel penalties.
  37 //! let scorer = Scorer::new(ScoringParameters {
  38 //!     base_penalty_msat: 1000,
  39 //!     failure_penalty_msat: 2 * 1024 * 1000,
  40 //!     ..ScoringParameters::default()
  41 //! });
  42 //!
  43 //! let route = find_route(&payer, &params, &network_graph, None, &logger, &scorer);
  44 //! # }
  45 //! ```
  46 //!
  47 //! [`find_route`]: crate::routing::router::find_route
  48
  49 use routing;
  50
  51 use routing::network_graph::NodeId;
  52 use routing::router::RouteHop;
  53
  54 use prelude::*;
  55 use core::time::Duration;
  56
  57 /// [`routing::Score`] implementation that provides reasonable default behavior.
  58 ///
  59 /// Used to apply a fixed penalty to each channel, thus avoiding long paths when shorter paths with
  60 /// slightly higher fees are available. Will further penalize channels that fail to relay payments.
  61 ///
  62 /// See [module-level documentation] for usage.
  63 ///
  64 /// [module-level documentation]: crate::routing::scorer
  65 pub type Scorer = ScorerUsingTime::<DefaultTime>;
  66
  67 /// Time used by [`Scorer`].
  68 #[cfg(not(feature = "no-std"))]
  69 pub type DefaultTime = std::time::Instant;
  70
  71 /// Time used by [`Scorer`].
  72 #[cfg(feature = "no-std")]
  73 pub type DefaultTime = Eternity;
  74
  75 /// [`routing::Score`] implementation parameterized by [`Time`].
  76 ///
  77 /// See [`Scorer`] for details.
  78 pub struct ScorerUsingTime<T: Time> {
  79         params: ScoringParameters,
  80         // TODO: Remove entries of closed channels.
  81         channel_failures: HashMap<u64, ChannelFailure<T>>,
  82 }
  83
  84 /// Parameters for configuring [`Scorer`].
  85 pub struct ScoringParameters {
  86         /// A fixed penalty in msats to apply to each channel.
  87         pub base_penalty_msat: u64,
  88
  89         /// A penalty in msats to apply to a channel upon failing to relay a payment.
  90         ///
  91         /// This accumulates for each failure but may be reduced over time based on
  92         /// [`failure_penalty_half_life`].
  93         ///
  94         /// [`failure_penalty_half_life`]: Self::failure_penalty_half_life
  95         pub failure_penalty_msat: u64,
  96
  97         /// The time required to elapse before any accumulated [`failure_penalty_msat`] penalties are
  98         /// cut in half.
  99         ///
 100         /// # Note
 101         ///
 102         /// When time is an [`Eternity`], as is default when enabling feature `no-std`, it will never
 103         /// elapse. Therefore, this penalty will never decay.
 104         ///
 105         /// [`failure_penalty_msat`]: Self::failure_penalty_msat
 106         pub failure_penalty_half_life: Duration,
 107 }
 108
 109 /// Accounting for penalties against a channel for failing to relay any payments.
 110 ///
 111 /// Penalties decay over time, though accumulate as more failures occur.
 112 struct ChannelFailure<T: Time> {
 113         /// Accumulated penalty in msats for the channel as of `last_failed`.
 114         undecayed_penalty_msat: u64,
 115
 116         /// Last time the channel failed. Used to decay `undecayed_penalty_msat`.
 117         last_failed: T,
 118 }
 119
 120 /// A measurement of time.
 121 pub trait Time {
 122         /// Returns an instance corresponding to the current moment.
 123         fn now() -> Self;
 124
 125         /// Returns the amount of time elapsed since `self` was created.
 126         fn elapsed(&self) -> Duration;
 127 }
 128
 129 impl<T: Time> ScorerUsingTime<T> {
 130         /// Creates a new scorer using the given scoring parameters.
 131         pub fn new(params: ScoringParameters) -> Self {
 132                 Self {
 133                         params,
 134                         channel_failures: HashMap::new(),
 135                 }
 136         }
 137
 138         /// Creates a new scorer using `penalty_msat` as a fixed channel penalty.
 139         #[cfg(any(test, feature = "fuzztarget", feature = "_test_utils"))]
 140         pub fn with_fixed_penalty(penalty_msat: u64) -> Self {
 141                 Self::new(ScoringParameters {
 142                         base_penalty_msat: penalty_msat,
 143                         failure_penalty_msat: 0,
 144                         failure_penalty_half_life: Duration::from_secs(0),
 145                 })
 146         }
 147 }
 148
 149 impl<T: Time> ChannelFailure<T> {
 150         fn new(failure_penalty_msat: u64) -> Self {
 151                 Self {
 152                         undecayed_penalty_msat: failure_penalty_msat,
 153                         last_failed: T::now(),
 154                 }
 155         }
 156
 157         fn add_penalty(&mut self, failure_penalty_msat: u64, half_life: Duration) {
 158                 self.undecayed_penalty_msat = self.decayed_penalty_msat(half_life) + failure_penalty_msat;
 159                 self.last_failed = T::now();
 160         }
 161
 162         fn decayed_penalty_msat(&self, half_life: Duration) -> u64 {
 163                 let decays = self.last_failed.elapsed().as_secs().checked_div(half_life.as_secs());
 164                 match decays {
 165                         Some(decays) => self.undecayed_penalty_msat >> decays,
 166                         None => 0,
 167                 }
 168         }
 169 }
 170
 171 impl<T: Time> Default for ScorerUsingTime<T> {
 172         fn default() -> Self {
 173                 Self::new(ScoringParameters::default())
 174         }
 175 }
 176
 177 impl Default for ScoringParameters {
 178         fn default() -> Self {
 179                 Self {
 180                         base_penalty_msat: 500,
 181                         failure_penalty_msat: 1024 * 1000,
 182                         failure_penalty_half_life: Duration::from_secs(3600),
 183                 }
 184         }
 185 }
 186
 187 impl<T: Time> routing::Score for ScorerUsingTime<T> {
 188         fn channel_penalty_msat(
 189                 &self, short_channel_id: u64, _source: &NodeId, _target: &NodeId
 190         ) -> u64 {
 191                 let failure_penalty_msat = self.channel_failures
 192                         .get(&short_channel_id)
 193                         .map_or(0, |value| value.decayed_penalty_msat(self.params.failure_penalty_half_life));
 194
 195                 self.params.base_penalty_msat + failure_penalty_msat
 196         }
 197
 198         fn payment_path_failed(&mut self, _path: &Vec<RouteHop>, short_channel_id: u64) {
 199                 let failure_penalty_msat = self.params.failure_penalty_msat;
 200                 let half_life = self.params.failure_penalty_half_life;
 201                 self.channel_failures
 202                         .entry(short_channel_id)
 203                         .and_modify(|failure| failure.add_penalty(failure_penalty_msat, half_life))
 204                         .or_insert_with(|| ChannelFailure::new(failure_penalty_msat));
 205         }
 206 }
 207
 208 #[cfg(not(feature = "no-std"))]
 209 impl Time for std::time::Instant {
 210         fn now() -> Self {
 211                 std::time::Instant::now()
 212         }
 213
 214         fn elapsed(&self) -> Duration {
 215                 std::time::Instant::elapsed(self)
 216         }
 217 }
 218
 219 /// A state in which time has no meaning.
 220 pub struct Eternity;
 221
 222 impl Time for Eternity {
 223         fn now() -> Self {
 224                 Self
 225         }
 226
 227         fn elapsed(&self) -> Duration {
 228                 Duration::from_secs(0)
 229         }
 230 }