_ 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 //! # Note
  48 //!
  49 //! If persisting [`Scorer`], it must be restored using the same [`Time`] parameterization. Using a
  50 //! different type results in undefined behavior. Specifically, persisting when built with feature
  51 //! `no-std` and restoring without it, or vice versa, uses different types and thus is undefined.
  52 //!
  53 //! [`find_route`]: crate::routing::router::find_route
  54
  55 use routing;
  56
  57 use ln::msgs::DecodeError;
  58 use routing::network_graph::NodeId;
  59 use routing::router::RouteHop;
  60 use util::ser::{Readable, Writeable, Writer};
  61
  62 use prelude::*;
  63 use core::ops::Sub;
  64 use core::time::Duration;
  65 use io::{self, Read};
  66
  67 /// [`routing::Score`] implementation that provides reasonable default behavior.
  68 ///
  69 /// Used to apply a fixed penalty to each channel, thus avoiding long paths when shorter paths with
  70 /// slightly higher fees are available. Will further penalize channels that fail to relay payments.
  71 ///
  72 /// See [module-level documentation] for usage.
  73 ///
  74 /// [module-level documentation]: crate::routing::scorer
  75 pub type Scorer = ScorerUsingTime::<DefaultTime>;
  76
  77 /// Time used by [`Scorer`].
  78 #[cfg(not(feature = "no-std"))]
  79 pub type DefaultTime = std::time::Instant;
  80
  81 /// Time used by [`Scorer`].
  82 #[cfg(feature = "no-std")]
  83 pub type DefaultTime = Eternity;
  84
  85 /// [`routing::Score`] implementation parameterized by [`Time`].
  86 ///
  87 /// See [`Scorer`] for details.
  88 ///
  89 /// # Note
  90 ///
  91 /// Mixing [`Time`] types between serialization and deserialization results in undefined behavior.
  92 pub struct ScorerUsingTime<T: Time> {
  93         params: ScoringParameters,
  94         // TODO: Remove entries of closed channels.
  95         channel_failures: HashMap<u64, ChannelFailure<T>>,
  96 }
  97
  98 /// Parameters for configuring [`Scorer`].
  99 pub struct ScoringParameters {
 100         /// A fixed penalty in msats to apply to each channel.
 101         pub base_penalty_msat: u64,
 102
 103         /// A penalty in msats to apply to a channel upon failing to relay a payment.
 104         ///
 105         /// This accumulates for each failure but may be reduced over time based on
 106         /// [`failure_penalty_half_life`].
 107         ///
 108         /// [`failure_penalty_half_life`]: Self::failure_penalty_half_life
 109         pub failure_penalty_msat: u64,
 110
 111         /// The time required to elapse before any accumulated [`failure_penalty_msat`] penalties are
 112         /// cut in half.
 113         ///
 114         /// # Note
 115         ///
 116         /// When time is an [`Eternity`], as is default when enabling feature `no-std`, it will never
 117         /// elapse. Therefore, this penalty will never decay.
 118         ///
 119         /// [`failure_penalty_msat`]: Self::failure_penalty_msat
 120         pub failure_penalty_half_life: Duration,
 121 }
 122
 123 impl_writeable_tlv_based!(ScoringParameters, {
 124         (0, base_penalty_msat, required),
 125         (2, failure_penalty_msat, required),
 126         (4, failure_penalty_half_life, required),
 127 });
 128
 129 /// Accounting for penalties against a channel for failing to relay any payments.
 130 ///
 131 /// Penalties decay over time, though accumulate as more failures occur.
 132 struct ChannelFailure<T: Time> {
 133         /// Accumulated penalty in msats for the channel as of `last_failed`.
 134         undecayed_penalty_msat: u64,
 135
 136         /// Last time the channel failed. Used to decay `undecayed_penalty_msat`.
 137         last_failed: T,
 138 }
 139
 140 /// A measurement of time.
 141 pub trait Time: Sub<Duration, Output = Self> where Self: Sized {
 142         /// Returns an instance corresponding to the current moment.
 143         fn now() -> Self;
 144
 145         /// Returns the amount of time elapsed since `self` was created.
 146         fn elapsed(&self) -> Duration;
 147
 148         /// Returns the amount of time passed since the beginning of [`Time`].
 149         ///
 150         /// Used during (de-)serialization.
 151         fn duration_since_epoch() -> Duration;
 152 }
 153
 154 impl<T: Time> ScorerUsingTime<T> {
 155         /// Creates a new scorer using the given scoring parameters.
 156         pub fn new(params: ScoringParameters) -> Self {
 157                 Self {
 158                         params,
 159                         channel_failures: HashMap::new(),
 160                 }
 161         }
 162
 163         /// Creates a new scorer using `penalty_msat` as a fixed channel penalty.
 164         #[cfg(any(test, feature = "fuzztarget", feature = "_test_utils"))]
 165         pub fn with_fixed_penalty(penalty_msat: u64) -> Self {
 166                 Self::new(ScoringParameters {
 167                         base_penalty_msat: penalty_msat,
 168                         failure_penalty_msat: 0,
 169                         failure_penalty_half_life: Duration::from_secs(0),
 170                 })
 171         }
 172 }
 173
 174 impl<T: Time> ChannelFailure<T> {
 175         fn new(failure_penalty_msat: u64) -> Self {
 176                 Self {
 177                         undecayed_penalty_msat: failure_penalty_msat,
 178                         last_failed: T::now(),
 179                 }
 180         }
 181
 182         fn add_penalty(&mut self, failure_penalty_msat: u64, half_life: Duration) {
 183                 self.undecayed_penalty_msat = self.decayed_penalty_msat(half_life) + failure_penalty_msat;
 184                 self.last_failed = T::now();
 185         }
 186
 187         fn decayed_penalty_msat(&self, half_life: Duration) -> u64 {
 188                 let decays = self.last_failed.elapsed().as_secs().checked_div(half_life.as_secs());
 189                 match decays {
 190                         Some(decays) => self.undecayed_penalty_msat >> decays,
 191                         None => 0,
 192                 }
 193         }
 194 }
 195
 196 impl<T: Time> Default for ScorerUsingTime<T> {
 197         fn default() -> Self {
 198                 Self::new(ScoringParameters::default())
 199         }
 200 }
 201
 202 impl Default for ScoringParameters {
 203         fn default() -> Self {
 204                 Self {
 205                         base_penalty_msat: 500,
 206                         failure_penalty_msat: 1024 * 1000,
 207                         failure_penalty_half_life: Duration::from_secs(3600),
 208                 }
 209         }
 210 }
 211
 212 impl<T: Time> routing::Score for ScorerUsingTime<T> {
 213         fn channel_penalty_msat(
 214                 &self, short_channel_id: u64, _source: &NodeId, _target: &NodeId
 215         ) -> u64 {
 216                 let failure_penalty_msat = self.channel_failures
 217                         .get(&short_channel_id)
 218                         .map_or(0, |value| value.decayed_penalty_msat(self.params.failure_penalty_half_life));
 219
 220                 self.params.base_penalty_msat + failure_penalty_msat
 221         }
 222
 223         fn payment_path_failed(&mut self, _path: &[&RouteHop], short_channel_id: u64) {
 224                 let failure_penalty_msat = self.params.failure_penalty_msat;
 225                 let half_life = self.params.failure_penalty_half_life;
 226                 self.channel_failures
 227                         .entry(short_channel_id)
 228                         .and_modify(|failure| failure.add_penalty(failure_penalty_msat, half_life))
 229                         .or_insert_with(|| ChannelFailure::new(failure_penalty_msat));
 230         }
 231 }
 232
 233 #[cfg(not(feature = "no-std"))]
 234 impl Time for std::time::Instant {
 235         fn now() -> Self {
 236                 std::time::Instant::now()
 237         }
 238
 239         fn duration_since_epoch() -> Duration {
 240                 use std::time::SystemTime;
 241                 SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap()
 242         }
 243
 244         fn elapsed(&self) -> Duration {
 245                 std::time::Instant::elapsed(self)
 246         }
 247 }
 248
 249 /// A state in which time has no meaning.
 250 pub struct Eternity;
 251
 252 impl Time for Eternity {
 253         fn now() -> Self {
 254                 Self
 255         }
 256
 257         fn duration_since_epoch() -> Duration {
 258                 Duration::from_secs(0)
 259         }
 260
 261         fn elapsed(&self) -> Duration {
 262                 Duration::from_secs(0)
 263         }
 264 }
 265
 266 impl Sub<Duration> for Eternity {
 267         type Output = Self;
 268
 269         fn sub(self, _other: Duration) -> Self {
 270                 self
 271         }
 272 }
 273
 274 impl<T: Time> Writeable for ScorerUsingTime<T> {
 275         #[inline]
 276         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 277                 self.params.write(w)?;
 278                 self.channel_failures.write(w)?;
 279                 write_tlv_fields!(w, {});
 280                 Ok(())
 281         }
 282 }
 283
 284 impl<T: Time> Readable for ScorerUsingTime<T> {
 285         #[inline]
 286         fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
 287                 let res = Ok(Self {
 288                         params: Readable::read(r)?,
 289                         channel_failures: Readable::read(r)?,
 290                 });
 291                 read_tlv_fields!(r, {});
 292                 res
 293         }
 294 }
 295
 296 impl<T: Time> Writeable for ChannelFailure<T> {
 297         #[inline]
 298         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 299                 let duration_since_epoch = T::duration_since_epoch() - self.last_failed.elapsed();
 300                 write_tlv_fields!(w, {
 301                         (0, self.undecayed_penalty_msat, required),
 302                         (2, duration_since_epoch, required),
 303                 });
 304                 Ok(())
 305         }
 306 }
 307
 308 impl<T: Time> Readable for ChannelFailure<T> {
 309         #[inline]
 310         fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
 311                 let mut undecayed_penalty_msat = 0;
 312                 let mut duration_since_epoch = Duration::from_secs(0);
 313                 read_tlv_fields!(r, {
 314                         (0, undecayed_penalty_msat, required),
 315                         (2, duration_since_epoch, required),
 316                 });
 317                 Ok(Self {
 318                         undecayed_penalty_msat,
 319                         last_failed: T::now() - (T::duration_since_epoch() - duration_since_epoch),
 320                 })
 321         }
 322 }