_ Git - rust-lightning/blob - lightning-invoice/src/payment.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 //! A module for paying Lightning invoices.
  11 //!
  12 //! Defines an [`InvoicePayer`] utility for paying invoices, parameterized by [`Payer`] and
  13 //! [`Router`] traits. Implementations of [`Payer`] provide the payer's node id, channels, and means
  14 //! to send a payment over a [`Route`]. Implementations of [`Router`] find a [`Route`] between payer
  15 //! and payee using information provided by the payer and from the payee's [`Invoice`].
  16 //!
  17 //! [`InvoicePayer`] is capable of retrying failed payments. It accomplishes this by implementing
  18 //! [`EventHandler`] which decorates a user-provided handler. It will intercept any
  19 //! [`Event::PaymentPathFailed`] events and retry the failed paths for a fixed number of total
  20 //! attempts or until retry is no longer possible. In such a situation, [`InvoicePayer`] will pass
  21 //! along the events to the user-provided handler.
  22 //!
  23 //! # Example
  24 //!
  25 //! ```
  26 //! # extern crate lightning;
  27 //! # extern crate lightning_invoice;
  28 //! # extern crate secp256k1;
  29 //! #
  30 //! # use lightning::ln::{PaymentHash, PaymentSecret};
  31 //! # use lightning::ln::channelmanager::{ChannelDetails, PaymentId, PaymentSendFailure};
  32 //! # use lightning::ln::msgs::LightningError;
  33 //! # use lightning::routing;
  34 //! # use lightning::routing::network_graph::NodeId;
  35 //! # use lightning::routing::router::{Route, RouteHop, RouteParameters};
  36 //! # use lightning::util::events::{Event, EventHandler, EventsProvider};
  37 //! # use lightning::util::logger::{Logger, Record};
  38 //! # use lightning_invoice::Invoice;
  39 //! # use lightning_invoice::payment::{InvoicePayer, Payer, RetryAttempts, Router};
  40 //! # use secp256k1::key::PublicKey;
  41 //! # use std::cell::RefCell;
  42 //! # use std::ops::Deref;
  43 //! #
  44 //! # struct FakeEventProvider {}
  45 //! # impl EventsProvider for FakeEventProvider {
  46 //! #     fn process_pending_events<H: Deref>(&self, handler: H) where H::Target: EventHandler {}
  47 //! # }
  48 //! #
  49 //! # struct FakePayer {}
  50 //! # impl Payer for FakePayer {
  51 //! #     fn node_id(&self) -> PublicKey { unimplemented!() }
  52 //! #     fn first_hops(&self) -> Vec<ChannelDetails> { unimplemented!() }
  53 //! #     fn send_payment(
  54 //! #         &self, route: &Route, payment_hash: PaymentHash, payment_secret: &Option<PaymentSecret>
  55 //! #     ) -> Result<PaymentId, PaymentSendFailure> { unimplemented!() }
  56 //! #     fn retry_payment(
  57 //! #         &self, route: &Route, payment_id: PaymentId
  58 //! #     ) -> Result<(), PaymentSendFailure> { unimplemented!() }
  59 //! # }
  60 //! #
  61 //! # struct FakeRouter {};
  62 //! # impl<S: routing::Score> Router<S> for FakeRouter {
  63 //! #     fn find_route(
  64 //! #         &self, payer: &PublicKey, params: &RouteParameters,
  65 //! #         first_hops: Option<&[&ChannelDetails]>, scorer: &S
  66 //! #     ) -> Result<Route, LightningError> { unimplemented!() }
  67 //! # }
  68 //! #
  69 //! # struct FakeScorer {};
  70 //! # impl routing::Score for FakeScorer {
  71 //! #     fn channel_penalty_msat(
  72 //! #         &self, _short_channel_id: u64, _source: &NodeId, _target: &NodeId
  73 //! #     ) -> u64 { 0 }
  74 //! #     fn payment_path_failed(&mut self, _path: &Vec<RouteHop>, _short_channel_id: u64) {}
  75 //! # }
  76 //! #
  77 //! # struct FakeLogger {};
  78 //! # impl Logger for FakeLogger {
  79 //! #     fn log(&self, record: &Record) { unimplemented!() }
  80 //! # }
  81 //! #
  82 //! # fn main() {
  83 //! let event_handler = |event: &Event| {
  84 //!     match event {
  85 //!         Event::PaymentPathFailed { .. } => println!("payment failed after retries"),
  86 //!         Event::PaymentSent { .. } => println!("payment successful"),
  87 //!         _ => {},
  88 //!     }
  89 //! };
  90 //! # let payer = FakePayer {};
  91 //! # let router = FakeRouter {};
  92 //! # let scorer = RefCell::new(FakeScorer {});
  93 //! # let logger = FakeLogger {};
  94 //! let invoice_payer = InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
  95 //!
  96 //! let invoice = "...";
  97 //! let invoice = invoice.parse::<Invoice>().unwrap();
  98 //! invoice_payer.pay_invoice(&invoice).unwrap();
  99 //!
 100 //! # let event_provider = FakeEventProvider {};
 101 //! loop {
 102 //!     event_provider.process_pending_events(&invoice_payer);
 103 //! }
 104 //! # }
 105 //! ```
 106 //!
 107 //! # Note
 108 //!
 109 //! The [`Route`] is computed before each payment attempt. Any updates affecting path finding such
 110 //! as updates to the network graph or changes to channel scores should be applied prior to
 111 //! retries, typically by way of composing [`EventHandler`]s accordingly.
 112
 113 use crate::Invoice;
 114
 115 use bitcoin_hashes::Hash;
 116
 117 use lightning::ln::{PaymentHash, PaymentSecret};
 118 use lightning::ln::channelmanager::{ChannelDetails, PaymentId, PaymentSendFailure};
 119 use lightning::ln::msgs::LightningError;
 120 use lightning::routing;
 121 use lightning::routing::{LockableScore, Score};
 122 use lightning::routing::router::{Payee, Route, RouteParameters};
 123 use lightning::util::events::{Event, EventHandler};
 124 use lightning::util::logger::Logger;
 125
 126 use secp256k1::key::PublicKey;
 127
 128 use std::collections::hash_map::{self, HashMap};
 129 use std::ops::Deref;
 130 use std::sync::Mutex;
 131 use std::time::{Duration, SystemTime};
 132
 133 /// A utility for paying [`Invoice]`s.
 134 pub struct InvoicePayer<P: Deref, R, S: Deref, L: Deref, E>
 135 where
 136         P::Target: Payer,
 137         R: for <'a> Router<<<S as Deref>::Target as routing::LockableScore<'a>>::Locked>,
 138         S::Target: for <'a> routing::LockableScore<'a>,
 139         L::Target: Logger,
 140         E: EventHandler,
 141 {
 142         payer: P,
 143         router: R,
 144         scorer: S,
 145         logger: L,
 146         event_handler: E,
 147         payment_cache: Mutex<HashMap<PaymentHash, usize>>,
 148         retry_attempts: RetryAttempts,
 149 }
 150
 151 /// A trait defining behavior of an [`Invoice`] payer.
 152 pub trait Payer {
 153         /// Returns the payer's node id.
 154         fn node_id(&self) -> PublicKey;
 155
 156         /// Returns the payer's channels.
 157         fn first_hops(&self) -> Vec<ChannelDetails>;
 158
 159         /// Sends a payment over the Lightning Network using the given [`Route`].
 160         fn send_payment(
 161                 &self, route: &Route, payment_hash: PaymentHash, payment_secret: &Option<PaymentSecret>
 162         ) -> Result<PaymentId, PaymentSendFailure>;
 163
 164         /// Retries a failed payment path for the [`PaymentId`] using the given [`Route`].
 165         fn retry_payment(&self, route: &Route, payment_id: PaymentId) -> Result<(), PaymentSendFailure>;
 166 }
 167
 168 /// A trait defining behavior for routing an [`Invoice`] payment.
 169 pub trait Router<S: routing::Score> {
 170         /// Finds a [`Route`] between `payer` and `payee` for a payment with the given values.
 171         fn find_route(
 172                 &self, payer: &PublicKey, params: &RouteParameters, first_hops: Option<&[&ChannelDetails]>,
 173                 scorer: &S
 174         ) -> Result<Route, LightningError>;
 175 }
 176
 177 /// Number of attempts to retry payment path failures for an [`Invoice`].
 178 ///
 179 /// Note that this is the number of *path* failures, not full payment retries. For multi-path
 180 /// payments, if this is less than the total number of paths, we will never even retry all of the
 181 /// payment's paths.
 182 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 183 pub struct RetryAttempts(pub usize);
 184
 185 /// An error that may occur when making a payment.
 186 #[derive(Clone, Debug)]
 187 pub enum PaymentError {
 188         /// An error resulting from the provided [`Invoice`] or payment hash.
 189         Invoice(&'static str),
 190         /// An error occurring when finding a route.
 191         Routing(LightningError),
 192         /// An error occurring when sending a payment.
 193         Sending(PaymentSendFailure),
 194 }
 195
 196 impl<P: Deref, R, S: Deref, L: Deref, E> InvoicePayer<P, R, S, L, E>
 197 where
 198         P::Target: Payer,
 199         R: for <'a> Router<<<S as Deref>::Target as routing::LockableScore<'a>>::Locked>,
 200         S::Target: for <'a> routing::LockableScore<'a>,
 201         L::Target: Logger,
 202         E: EventHandler,
 203 {
 204         /// Creates an invoice payer that retries failed payment paths.
 205         ///
 206         /// Will forward any [`Event::PaymentPathFailed`] events to the decorated `event_handler` once
 207         /// `retry_attempts` has been exceeded for a given [`Invoice`].
 208         pub fn new(
 209                 payer: P, router: R, scorer: S, logger: L, event_handler: E, retry_attempts: RetryAttempts
 210         ) -> Self {
 211                 Self {
 212                         payer,
 213                         router,
 214                         scorer,
 215                         logger,
 216                         event_handler,
 217                         payment_cache: Mutex::new(HashMap::new()),
 218                         retry_attempts,
 219                 }
 220         }
 221
 222         /// Pays the given [`Invoice`], caching it for later use in case a retry is needed.
 223         ///
 224         /// You should ensure that the `invoice.payment_hash()` is unique and the same payment_hash has
 225         /// never been paid before. Because [`InvoicePayer`] is stateless no effort is made to do so
 226         /// for you.
 227         pub fn pay_invoice(&self, invoice: &Invoice) -> Result<PaymentId, PaymentError> {
 228                 if invoice.amount_milli_satoshis().is_none() {
 229                         Err(PaymentError::Invoice("amount missing"))
 230                 } else {
 231                         self.pay_invoice_internal(invoice, None)
 232                 }
 233         }
 234
 235         /// Pays the given zero-value [`Invoice`] using the given amount, caching it for later use in
 236         /// case a retry is needed.
 237         ///
 238         /// You should ensure that the `invoice.payment_hash()` is unique and the same payment_hash has
 239         /// never been paid before. Because [`InvoicePayer`] is stateless no effort is made to do so
 240         /// for you.
 241         pub fn pay_zero_value_invoice(
 242                 &self, invoice: &Invoice, amount_msats: u64
 243         ) -> Result<PaymentId, PaymentError> {
 244                 if invoice.amount_milli_satoshis().is_some() {
 245                         Err(PaymentError::Invoice("amount unexpected"))
 246                 } else {
 247                         self.pay_invoice_internal(invoice, Some(amount_msats))
 248                 }
 249         }
 250
 251         fn pay_invoice_internal(
 252                 &self, invoice: &Invoice, amount_msats: Option<u64>
 253         ) -> Result<PaymentId, PaymentError> {
 254                 debug_assert!(invoice.amount_milli_satoshis().is_some() ^ amount_msats.is_some());
 255                 let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
 256                 let mut payment_cache = self.payment_cache.lock().unwrap();
 257                 match payment_cache.entry(payment_hash) {
 258                         hash_map::Entry::Vacant(entry) => {
 259                                 let payer = self.payer.node_id();
 260                                 let mut payee = Payee::new(invoice.recover_payee_pub_key())
 261                                         .with_expiry_time(expiry_time_from_unix_epoch(&invoice).as_secs())
 262                                         .with_route_hints(invoice.route_hints());
 263                                 if let Some(features) = invoice.features() {
 264                                         payee = payee.with_features(features.clone());
 265                                 }
 266                                 let params = RouteParameters {
 267                                         payee,
 268                                         final_value_msat: invoice.amount_milli_satoshis().or(amount_msats).unwrap(),
 269                                         final_cltv_expiry_delta: invoice.min_final_cltv_expiry() as u32,
 270                                 };
 271                                 let first_hops = self.payer.first_hops();
 272                                 let route = self.router.find_route(
 273                                         &payer,
 274                                         &params,
 275                                         Some(&first_hops.iter().collect::<Vec<_>>()),
 276                                         &self.scorer.lock(),
 277                                 ).map_err(|e| PaymentError::Routing(e))?;
 278
 279                                 let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
 280                                 let payment_secret = Some(invoice.payment_secret().clone());
 281                                 let payment_id = self.payer.send_payment(&route, payment_hash, &payment_secret)
 282                                         .map_err(|e| PaymentError::Sending(e))?;
 283                                 entry.insert(0);
 284                                 Ok(payment_id)
 285                         },
 286                         hash_map::Entry::Occupied(_) => Err(PaymentError::Invoice("payment pending")),
 287                 }
 288         }
 289
 290         fn retry_payment(
 291                 &self, payment_id: PaymentId, params: &RouteParameters
 292         ) -> Result<(), PaymentError> {
 293                 let payer = self.payer.node_id();
 294                 let first_hops = self.payer.first_hops();
 295                 let route = self.router.find_route(
 296                         &payer, &params, Some(&first_hops.iter().collect::<Vec<_>>()),
 297                         &self.scorer.lock()
 298                 ).map_err(|e| PaymentError::Routing(e))?;
 299                 self.payer.retry_payment(&route, payment_id).map_err(|e| PaymentError::Sending(e))
 300         }
 301
 302         /// Removes the payment cached by the given payment hash.
 303         ///
 304         /// Should be called once a payment has failed or succeeded if not using [`InvoicePayer`] as an
 305         /// [`EventHandler`]. Otherwise, calling this method is unnecessary.
 306         pub fn remove_cached_payment(&self, payment_hash: &PaymentHash) {
 307                 self.payment_cache.lock().unwrap().remove(payment_hash);
 308         }
 309 }
 310
 311 fn expiry_time_from_unix_epoch(invoice: &Invoice) -> Duration {
 312         invoice.timestamp().duration_since(SystemTime::UNIX_EPOCH).unwrap() + invoice.expiry_time()
 313 }
 314
 315 fn has_expired(params: &RouteParameters) -> bool {
 316         if let Some(expiry_time) = params.payee.expiry_time {
 317                 Invoice::is_expired_from_epoch(&SystemTime::UNIX_EPOCH, Duration::from_secs(expiry_time))
 318         } else { false }
 319 }
 320
 321 impl<P: Deref, R, S: Deref, L: Deref, E> EventHandler for InvoicePayer<P, R, S, L, E>
 322 where
 323         P::Target: Payer,
 324         R: for <'a> Router<<<S as Deref>::Target as routing::LockableScore<'a>>::Locked>,
 325         S::Target: for <'a> routing::LockableScore<'a>,
 326         L::Target: Logger,
 327         E: EventHandler,
 328 {
 329         fn handle_event(&self, event: &Event) {
 330                 match event {
 331                         Event::PaymentPathFailed {
 332                                 payment_id, payment_hash, rejected_by_dest, path, short_channel_id, retry, ..
 333                         } => {
 334                                 if let Some(short_channel_id) = short_channel_id {
 335                                         self.scorer.lock().payment_path_failed(path, *short_channel_id);
 336                                 }
 337
 338                                 let mut payment_cache = self.payment_cache.lock().unwrap();
 339                                 let entry = loop {
 340                                         let entry = payment_cache.entry(*payment_hash);
 341                                         match entry {
 342                                                 hash_map::Entry::Occupied(_) => break entry,
 343                                                 hash_map::Entry::Vacant(entry) => entry.insert(0),
 344                                         };
 345                                 };
 346                                 if let hash_map::Entry::Occupied(mut entry) = entry {
 347                                         let max_payment_attempts = self.retry_attempts.0 + 1;
 348                                         let attempts = entry.get_mut();
 349                                         *attempts += 1;
 350
 351                                         if *rejected_by_dest {
 352                                                 log_trace!(self.logger, "Payment {} rejected by destination; not retrying (attempts: {})", log_bytes!(payment_hash.0), attempts);
 353                                         } else if payment_id.is_none() {
 354                                                 log_trace!(self.logger, "Payment {} has no id; not retrying (attempts: {})", log_bytes!(payment_hash.0), attempts);
 355                                         } else if *attempts >= max_payment_attempts {
 356                                                 log_trace!(self.logger, "Payment {} exceeded maximum attempts; not retrying (attempts: {})", log_bytes!(payment_hash.0), attempts);
 357                                         } else if retry.is_none() {
 358                                                 log_trace!(self.logger, "Payment {} missing retry params; not retrying (attempts: {})", log_bytes!(payment_hash.0), attempts);
 359                                         } else if has_expired(retry.as_ref().unwrap()) {
 360                                                 log_trace!(self.logger, "Invoice expired for payment {}; not retrying (attempts: {})", log_bytes!(payment_hash.0), attempts);
 361                                         } else if self.retry_payment(*payment_id.as_ref().unwrap(), retry.as_ref().unwrap()).is_err() {
 362                                                 log_trace!(self.logger, "Error retrying payment {}; not retrying (attempts: {})", log_bytes!(payment_hash.0), attempts);
 363                                         } else {
 364                                                 log_trace!(self.logger, "Payment {} failed; retrying (attempts: {})", log_bytes!(payment_hash.0), attempts);
 365                                                 return;
 366                                         }
 367
 368                                         // Either the payment was rejected, the maximum attempts were exceeded, or an
 369                                         // error occurred when attempting to retry.
 370                                         entry.remove();
 371                                 } else {
 372                                         unreachable!();
 373                                 }
 374                         },
 375                         Event::PaymentSent { payment_hash, .. } => {
 376                                 let mut payment_cache = self.payment_cache.lock().unwrap();
 377                                 let attempts = payment_cache
 378                                         .remove(payment_hash)
 379                                         .map_or(1, |attempts| attempts + 1);
 380                                 log_trace!(self.logger, "Payment {} succeeded (attempts: {})", log_bytes!(payment_hash.0), attempts);
 381                         },
 382                         _ => {},
 383                 }
 384
 385                 // Delegate to the decorated event handler unless the payment is retried.
 386                 self.event_handler.handle_event(event)
 387         }
 388 }
 389
 390 #[cfg(test)]
 391 mod tests {
 392         use super::*;
 393         use crate::{DEFAULT_EXPIRY_TIME, InvoiceBuilder, Currency};
 394         use bitcoin_hashes::sha256::Hash as Sha256;
 395         use lightning::ln::PaymentPreimage;
 396         use lightning::ln::features::{ChannelFeatures, NodeFeatures};
 397         use lightning::ln::msgs::{ErrorAction, LightningError};
 398         use lightning::routing::network_graph::NodeId;
 399         use lightning::routing::router::{Payee, Route, RouteHop};
 400         use lightning::util::test_utils::TestLogger;
 401         use lightning::util::errors::APIError;
 402         use lightning::util::events::Event;
 403         use secp256k1::{SecretKey, PublicKey, Secp256k1};
 404         use std::cell::RefCell;
 405         use std::time::{SystemTime, Duration};
 406
 407         fn invoice(payment_preimage: PaymentPreimage) -> Invoice {
 408                 let payment_hash = Sha256::hash(&payment_preimage.0);
 409                 let private_key = SecretKey::from_slice(&[42; 32]).unwrap();
 410                 InvoiceBuilder::new(Currency::Bitcoin)
 411                         .description("test".into())
 412                         .payment_hash(payment_hash)
 413                         .payment_secret(PaymentSecret([0; 32]))
 414                         .current_timestamp()
 415                         .min_final_cltv_expiry(144)
 416                         .amount_milli_satoshis(128)
 417                         .build_signed(|hash| {
 418                                 Secp256k1::new().sign_recoverable(hash, &private_key)
 419                         })
 420                         .unwrap()
 421         }
 422
 423         fn zero_value_invoice(payment_preimage: PaymentPreimage) -> Invoice {
 424                 let payment_hash = Sha256::hash(&payment_preimage.0);
 425                 let private_key = SecretKey::from_slice(&[42; 32]).unwrap();
 426                 InvoiceBuilder::new(Currency::Bitcoin)
 427                         .description("test".into())
 428                         .payment_hash(payment_hash)
 429                         .payment_secret(PaymentSecret([0; 32]))
 430                         .current_timestamp()
 431                         .min_final_cltv_expiry(144)
 432                         .build_signed(|hash| {
 433                                 Secp256k1::new().sign_recoverable(hash, &private_key)
 434                         })
 435                         .unwrap()
 436         }
 437
 438         fn expired_invoice(payment_preimage: PaymentPreimage) -> Invoice {
 439                 let payment_hash = Sha256::hash(&payment_preimage.0);
 440                 let private_key = SecretKey::from_slice(&[42; 32]).unwrap();
 441                 let timestamp = SystemTime::now()
 442                         .checked_sub(Duration::from_secs(DEFAULT_EXPIRY_TIME * 2))
 443                         .unwrap();
 444                 InvoiceBuilder::new(Currency::Bitcoin)
 445                         .description("test".into())
 446                         .payment_hash(payment_hash)
 447                         .payment_secret(PaymentSecret([0; 32]))
 448                         .timestamp(timestamp)
 449                         .min_final_cltv_expiry(144)
 450                         .amount_milli_satoshis(128)
 451                         .build_signed(|hash| {
 452                                 Secp256k1::new().sign_recoverable(hash, &private_key)
 453                         })
 454                         .unwrap()
 455         }
 456
 457         #[test]
 458         fn pays_invoice_on_first_attempt() {
 459                 let event_handled = core::cell::RefCell::new(false);
 460                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 461
 462                 let payment_preimage = PaymentPreimage([1; 32]);
 463                 let invoice = invoice(payment_preimage);
 464                 let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
 465
 466                 let payer = TestPayer::new();
 467                 let router = TestRouter {};
 468                 let scorer = RefCell::new(TestScorer::new());
 469                 let logger = TestLogger::new();
 470                 let invoice_payer =
 471                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(0));
 472
 473                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 474                 assert_eq!(*payer.attempts.borrow(), 1);
 475
 476                 invoice_payer.handle_event(&Event::PaymentSent {
 477                         payment_id, payment_preimage, payment_hash, fee_paid_msat: None
 478                 });
 479                 assert_eq!(*event_handled.borrow(), true);
 480                 assert_eq!(*payer.attempts.borrow(), 1);
 481         }
 482
 483         #[test]
 484         fn pays_invoice_on_retry() {
 485                 let event_handled = core::cell::RefCell::new(false);
 486                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 487
 488                 let payment_preimage = PaymentPreimage([1; 32]);
 489                 let invoice = invoice(payment_preimage);
 490                 let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
 491                 let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 492
 493                 let payer = TestPayer::new()
 494                         .expect_value_msat(final_value_msat)
 495                         .expect_value_msat(final_value_msat / 2);
 496                 let router = TestRouter {};
 497                 let scorer = RefCell::new(TestScorer::new());
 498                 let logger = TestLogger::new();
 499                 let invoice_payer =
 500                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
 501
 502                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 503                 assert_eq!(*payer.attempts.borrow(), 1);
 504
 505                 let event = Event::PaymentPathFailed {
 506                         payment_id,
 507                         payment_hash,
 508                         network_update: None,
 509                         rejected_by_dest: false,
 510                         all_paths_failed: false,
 511                         path: TestRouter::path_for_value(final_value_msat),
 512                         short_channel_id: None,
 513                         retry: Some(TestRouter::retry_for_invoice(&invoice)),
 514                 };
 515                 invoice_payer.handle_event(&event);
 516                 assert_eq!(*event_handled.borrow(), false);
 517                 assert_eq!(*payer.attempts.borrow(), 2);
 518
 519                 invoice_payer.handle_event(&Event::PaymentSent {
 520                         payment_id, payment_preimage, payment_hash, fee_paid_msat: None
 521                 });
 522                 assert_eq!(*event_handled.borrow(), true);
 523                 assert_eq!(*payer.attempts.borrow(), 2);
 524         }
 525
 526         #[test]
 527         fn retries_payment_path_for_unknown_payment() {
 528                 let event_handled = core::cell::RefCell::new(false);
 529                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 530
 531                 let payment_preimage = PaymentPreimage([1; 32]);
 532                 let invoice = invoice(payment_preimage);
 533                 let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
 534                 let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 535
 536                 let payer = TestPayer::new();
 537                 let router = TestRouter {};
 538                 let scorer = RefCell::new(TestScorer::new());
 539                 let logger = TestLogger::new();
 540                 let invoice_payer =
 541                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
 542
 543                 let payment_id = Some(PaymentId([1; 32]));
 544                 let event = Event::PaymentPathFailed {
 545                         payment_id,
 546                         payment_hash,
 547                         network_update: None,
 548                         rejected_by_dest: false,
 549                         all_paths_failed: false,
 550                         path: TestRouter::path_for_value(final_value_msat),
 551                         short_channel_id: None,
 552                         retry: Some(TestRouter::retry_for_invoice(&invoice)),
 553                 };
 554                 invoice_payer.handle_event(&event);
 555                 assert_eq!(*event_handled.borrow(), false);
 556                 assert_eq!(*payer.attempts.borrow(), 1);
 557
 558                 invoice_payer.handle_event(&event);
 559                 assert_eq!(*event_handled.borrow(), false);
 560                 assert_eq!(*payer.attempts.borrow(), 2);
 561
 562                 invoice_payer.handle_event(&Event::PaymentSent {
 563                         payment_id, payment_preimage, payment_hash, fee_paid_msat: None
 564                 });
 565                 assert_eq!(*event_handled.borrow(), true);
 566                 assert_eq!(*payer.attempts.borrow(), 2);
 567         }
 568
 569         #[test]
 570         fn fails_paying_invoice_after_max_retries() {
 571                 let event_handled = core::cell::RefCell::new(false);
 572                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 573
 574                 let payment_preimage = PaymentPreimage([1; 32]);
 575                 let invoice = invoice(payment_preimage);
 576                 let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 577
 578                 let payer = TestPayer::new()
 579                         .expect_value_msat(final_value_msat)
 580                         .expect_value_msat(final_value_msat / 2)
 581                         .expect_value_msat(final_value_msat / 2);
 582                 let router = TestRouter {};
 583                 let scorer = RefCell::new(TestScorer::new());
 584                 let logger = TestLogger::new();
 585                 let invoice_payer =
 586                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
 587
 588                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 589                 assert_eq!(*payer.attempts.borrow(), 1);
 590
 591                 let event = Event::PaymentPathFailed {
 592                         payment_id,
 593                         payment_hash: PaymentHash(invoice.payment_hash().clone().into_inner()),
 594                         network_update: None,
 595                         rejected_by_dest: false,
 596                         all_paths_failed: true,
 597                         path: TestRouter::path_for_value(final_value_msat),
 598                         short_channel_id: None,
 599                         retry: Some(TestRouter::retry_for_invoice(&invoice)),
 600                 };
 601                 invoice_payer.handle_event(&event);
 602                 assert_eq!(*event_handled.borrow(), false);
 603                 assert_eq!(*payer.attempts.borrow(), 2);
 604
 605                 let event = Event::PaymentPathFailed {
 606                         payment_id,
 607                         payment_hash: PaymentHash(invoice.payment_hash().clone().into_inner()),
 608                         network_update: None,
 609                         rejected_by_dest: false,
 610                         all_paths_failed: false,
 611                         path: TestRouter::path_for_value(final_value_msat / 2),
 612                         short_channel_id: None,
 613                         retry: Some(RouteParameters {
 614                                 final_value_msat: final_value_msat / 2, ..TestRouter::retry_for_invoice(&invoice)
 615                         }),
 616                 };
 617                 invoice_payer.handle_event(&event);
 618                 assert_eq!(*event_handled.borrow(), false);
 619                 assert_eq!(*payer.attempts.borrow(), 3);
 620
 621                 invoice_payer.handle_event(&event);
 622                 assert_eq!(*event_handled.borrow(), true);
 623                 assert_eq!(*payer.attempts.borrow(), 3);
 624         }
 625
 626         #[test]
 627         fn fails_paying_invoice_with_missing_retry_params() {
 628                 let event_handled = core::cell::RefCell::new(false);
 629                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 630
 631                 let payer = TestPayer::new();
 632                 let router = TestRouter {};
 633                 let scorer = RefCell::new(TestScorer::new());
 634                 let logger = TestLogger::new();
 635                 let invoice_payer =
 636                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
 637
 638                 let payment_preimage = PaymentPreimage([1; 32]);
 639                 let invoice = invoice(payment_preimage);
 640                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 641                 assert_eq!(*payer.attempts.borrow(), 1);
 642
 643                 let event = Event::PaymentPathFailed {
 644                         payment_id,
 645                         payment_hash: PaymentHash(invoice.payment_hash().clone().into_inner()),
 646                         network_update: None,
 647                         rejected_by_dest: false,
 648                         all_paths_failed: false,
 649                         path: vec![],
 650                         short_channel_id: None,
 651                         retry: None,
 652                 };
 653                 invoice_payer.handle_event(&event);
 654                 assert_eq!(*event_handled.borrow(), true);
 655                 assert_eq!(*payer.attempts.borrow(), 1);
 656         }
 657
 658         #[test]
 659         fn fails_paying_invoice_after_expiration() {
 660                 let event_handled = core::cell::RefCell::new(false);
 661                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 662
 663                 let payer = TestPayer::new();
 664                 let router = TestRouter {};
 665                 let scorer = RefCell::new(TestScorer::new());
 666                 let logger = TestLogger::new();
 667                 let invoice_payer =
 668                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
 669
 670                 let payment_preimage = PaymentPreimage([1; 32]);
 671                 let invoice = expired_invoice(payment_preimage);
 672                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 673                 assert_eq!(*payer.attempts.borrow(), 1);
 674
 675                 let event = Event::PaymentPathFailed {
 676                         payment_id,
 677                         payment_hash: PaymentHash(invoice.payment_hash().clone().into_inner()),
 678                         network_update: None,
 679                         rejected_by_dest: false,
 680                         all_paths_failed: false,
 681                         path: vec![],
 682                         short_channel_id: None,
 683                         retry: Some(TestRouter::retry_for_invoice(&invoice)),
 684                 };
 685                 invoice_payer.handle_event(&event);
 686                 assert_eq!(*event_handled.borrow(), true);
 687                 assert_eq!(*payer.attempts.borrow(), 1);
 688         }
 689
 690         #[test]
 691         fn fails_paying_invoice_after_retry_error() {
 692                 let event_handled = core::cell::RefCell::new(false);
 693                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 694
 695                 let payment_preimage = PaymentPreimage([1; 32]);
 696                 let invoice = invoice(payment_preimage);
 697                 let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 698
 699                 let payer = TestPayer::new()
 700                         .fails_on_attempt(2)
 701                         .expect_value_msat(final_value_msat);
 702                 let router = TestRouter {};
 703                 let scorer = RefCell::new(TestScorer::new());
 704                 let logger = TestLogger::new();
 705                 let invoice_payer =
 706                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
 707
 708                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 709                 assert_eq!(*payer.attempts.borrow(), 1);
 710
 711                 let event = Event::PaymentPathFailed {
 712                         payment_id,
 713                         payment_hash: PaymentHash(invoice.payment_hash().clone().into_inner()),
 714                         network_update: None,
 715                         rejected_by_dest: false,
 716                         all_paths_failed: false,
 717                         path: TestRouter::path_for_value(final_value_msat / 2),
 718                         short_channel_id: None,
 719                         retry: Some(TestRouter::retry_for_invoice(&invoice)),
 720                 };
 721                 invoice_payer.handle_event(&event);
 722                 assert_eq!(*event_handled.borrow(), true);
 723                 assert_eq!(*payer.attempts.borrow(), 2);
 724         }
 725
 726         #[test]
 727         fn fails_paying_invoice_after_rejected_by_payee() {
 728                 let event_handled = core::cell::RefCell::new(false);
 729                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 730
 731                 let payer = TestPayer::new();
 732                 let router = TestRouter {};
 733                 let scorer = RefCell::new(TestScorer::new());
 734                 let logger = TestLogger::new();
 735                 let invoice_payer =
 736                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
 737
 738                 let payment_preimage = PaymentPreimage([1; 32]);
 739                 let invoice = invoice(payment_preimage);
 740                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 741                 assert_eq!(*payer.attempts.borrow(), 1);
 742
 743                 let event = Event::PaymentPathFailed {
 744                         payment_id,
 745                         payment_hash: PaymentHash(invoice.payment_hash().clone().into_inner()),
 746                         network_update: None,
 747                         rejected_by_dest: true,
 748                         all_paths_failed: false,
 749                         path: vec![],
 750                         short_channel_id: None,
 751                         retry: Some(TestRouter::retry_for_invoice(&invoice)),
 752                 };
 753                 invoice_payer.handle_event(&event);
 754                 assert_eq!(*event_handled.borrow(), true);
 755                 assert_eq!(*payer.attempts.borrow(), 1);
 756         }
 757
 758         #[test]
 759         fn fails_repaying_invoice_with_pending_payment() {
 760                 let event_handled = core::cell::RefCell::new(false);
 761                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 762
 763                 let payer = TestPayer::new();
 764                 let router = TestRouter {};
 765                 let scorer = RefCell::new(TestScorer::new());
 766                 let logger = TestLogger::new();
 767                 let invoice_payer =
 768                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(0));
 769
 770                 let payment_preimage = PaymentPreimage([1; 32]);
 771                 let invoice = invoice(payment_preimage);
 772                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 773
 774                 // Cannot repay an invoice pending payment.
 775                 match invoice_payer.pay_invoice(&invoice) {
 776                         Err(PaymentError::Invoice("payment pending")) => {},
 777                         Err(_) => panic!("unexpected error"),
 778                         Ok(_) => panic!("expected invoice error"),
 779                 }
 780
 781                 // Can repay an invoice once cleared from cache.
 782                 let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
 783                 invoice_payer.remove_cached_payment(&payment_hash);
 784                 assert!(invoice_payer.pay_invoice(&invoice).is_ok());
 785
 786                 // Cannot retry paying an invoice if cleared from cache.
 787                 invoice_payer.remove_cached_payment(&payment_hash);
 788                 let event = Event::PaymentPathFailed {
 789                         payment_id,
 790                         payment_hash,
 791                         network_update: None,
 792                         rejected_by_dest: false,
 793                         all_paths_failed: false,
 794                         path: vec![],
 795                         short_channel_id: None,
 796                         retry: Some(TestRouter::retry_for_invoice(&invoice)),
 797                 };
 798                 invoice_payer.handle_event(&event);
 799                 assert_eq!(*event_handled.borrow(), true);
 800         }
 801
 802         #[test]
 803         fn fails_paying_invoice_with_routing_errors() {
 804                 let payer = TestPayer::new();
 805                 let router = FailingRouter {};
 806                 let scorer = RefCell::new(TestScorer::new());
 807                 let logger = TestLogger::new();
 808                 let invoice_payer =
 809                         InvoicePayer::new(&payer, router, &scorer, &logger, |_: &_| {}, RetryAttempts(0));
 810
 811                 let payment_preimage = PaymentPreimage([1; 32]);
 812                 let invoice = invoice(payment_preimage);
 813                 match invoice_payer.pay_invoice(&invoice) {
 814                         Err(PaymentError::Routing(_)) => {},
 815                         Err(_) => panic!("unexpected error"),
 816                         Ok(_) => panic!("expected routing error"),
 817                 }
 818         }
 819
 820         #[test]
 821         fn fails_paying_invoice_with_sending_errors() {
 822                 let payer = TestPayer::new().fails_on_attempt(1);
 823                 let router = TestRouter {};
 824                 let scorer = RefCell::new(TestScorer::new());
 825                 let logger = TestLogger::new();
 826                 let invoice_payer =
 827                         InvoicePayer::new(&payer, router, &scorer, &logger, |_: &_| {}, RetryAttempts(0));
 828
 829                 let payment_preimage = PaymentPreimage([1; 32]);
 830                 let invoice = invoice(payment_preimage);
 831                 match invoice_payer.pay_invoice(&invoice) {
 832                         Err(PaymentError::Sending(_)) => {},
 833                         Err(_) => panic!("unexpected error"),
 834                         Ok(_) => panic!("expected sending error"),
 835                 }
 836         }
 837
 838         #[test]
 839         fn pays_zero_value_invoice_using_amount() {
 840                 let event_handled = core::cell::RefCell::new(false);
 841                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 842
 843                 let payment_preimage = PaymentPreimage([1; 32]);
 844                 let invoice = zero_value_invoice(payment_preimage);
 845                 let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
 846                 let final_value_msat = 100;
 847
 848                 let payer = TestPayer::new().expect_value_msat(final_value_msat);
 849                 let router = TestRouter {};
 850                 let scorer = RefCell::new(TestScorer::new());
 851                 let logger = TestLogger::new();
 852                 let invoice_payer =
 853                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(0));
 854
 855                 let payment_id =
 856                         Some(invoice_payer.pay_zero_value_invoice(&invoice, final_value_msat).unwrap());
 857                 assert_eq!(*payer.attempts.borrow(), 1);
 858
 859                 invoice_payer.handle_event(&Event::PaymentSent {
 860                         payment_id, payment_preimage, payment_hash, fee_paid_msat: None
 861                 });
 862                 assert_eq!(*event_handled.borrow(), true);
 863                 assert_eq!(*payer.attempts.borrow(), 1);
 864         }
 865
 866         #[test]
 867         fn fails_paying_zero_value_invoice_with_amount() {
 868                 let event_handled = core::cell::RefCell::new(false);
 869                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 870
 871                 let payer = TestPayer::new();
 872                 let router = TestRouter {};
 873                 let scorer = RefCell::new(TestScorer::new());
 874                 let logger = TestLogger::new();
 875                 let invoice_payer =
 876                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(0));
 877
 878                 let payment_preimage = PaymentPreimage([1; 32]);
 879                 let invoice = invoice(payment_preimage);
 880
 881                 // Cannot repay an invoice pending payment.
 882                 match invoice_payer.pay_zero_value_invoice(&invoice, 100) {
 883                         Err(PaymentError::Invoice("amount unexpected")) => {},
 884                         Err(_) => panic!("unexpected error"),
 885                         Ok(_) => panic!("expected invoice error"),
 886                 }
 887         }
 888
 889         #[test]
 890         fn scores_failed_channel() {
 891                 let event_handled = core::cell::RefCell::new(false);
 892                 let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
 893
 894                 let payment_preimage = PaymentPreimage([1; 32]);
 895                 let invoice = invoice(payment_preimage);
 896                 let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
 897                 let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 898                 let path = TestRouter::path_for_value(final_value_msat);
 899                 let short_channel_id = Some(path[0].short_channel_id);
 900
 901                 // Expect that scorer is given short_channel_id upon handling the event.
 902                 let payer = TestPayer::new();
 903                 let router = TestRouter {};
 904                 let scorer = RefCell::new(TestScorer::new().expect_channel_failure(short_channel_id.unwrap()));
 905                 let logger = TestLogger::new();
 906                 let invoice_payer =
 907                         InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, RetryAttempts(2));
 908
 909                 let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 910                 let event = Event::PaymentPathFailed {
 911                         payment_id,
 912                         payment_hash,
 913                         network_update: None,
 914                         rejected_by_dest: false,
 915                         all_paths_failed: false,
 916                         path,
 917                         short_channel_id,
 918                         retry: Some(TestRouter::retry_for_invoice(&invoice)),
 919                 };
 920                 invoice_payer.handle_event(&event);
 921         }
 922
 923         struct TestRouter;
 924
 925         impl TestRouter {
 926                 fn route_for_value(final_value_msat: u64) -> Route {
 927                         Route {
 928                                 paths: vec![
 929                                         vec![RouteHop {
 930                                                 pubkey: PublicKey::from_slice(&hex::decode("02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619").unwrap()[..]).unwrap(),
 931                                                 channel_features: ChannelFeatures::empty(),
 932                                                 node_features: NodeFeatures::empty(),
 933                                                 short_channel_id: 0, fee_msat: final_value_msat / 2, cltv_expiry_delta: 144
 934                                         }],
 935                                         vec![RouteHop {
 936                                                 pubkey: PublicKey::from_slice(&hex::decode("0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c").unwrap()[..]).unwrap(),
 937                                                 channel_features: ChannelFeatures::empty(),
 938                                                 node_features: NodeFeatures::empty(),
 939                                                 short_channel_id: 1, fee_msat: final_value_msat / 2, cltv_expiry_delta: 144
 940                                         }],
 941                                 ],
 942                                 payee: None,
 943                         }
 944                 }
 945
 946                 fn path_for_value(final_value_msat: u64) -> Vec<RouteHop> {
 947                         TestRouter::route_for_value(final_value_msat).paths[0].clone()
 948                 }
 949
 950                 fn retry_for_invoice(invoice: &Invoice) -> RouteParameters {
 951                         let mut payee = Payee::new(invoice.recover_payee_pub_key())
 952                                 .with_expiry_time(expiry_time_from_unix_epoch(invoice).as_secs())
 953                                 .with_route_hints(invoice.route_hints());
 954                         if let Some(features) = invoice.features() {
 955                                 payee = payee.with_features(features.clone());
 956                         }
 957                         let final_value_msat = invoice.amount_milli_satoshis().unwrap() / 2;
 958                         RouteParameters {
 959                                 payee,
 960                                 final_value_msat,
 961                                 final_cltv_expiry_delta: invoice.min_final_cltv_expiry() as u32,
 962                         }
 963                 }
 964         }
 965
 966         impl<S: routing::Score> Router<S> for TestRouter {
 967                 fn find_route(
 968                         &self,
 969                         _payer: &PublicKey,
 970                         params: &RouteParameters,
 971                         _first_hops: Option<&[&ChannelDetails]>,
 972                         _scorer: &S,
 973                 ) -> Result<Route, LightningError> {
 974                         Ok(Route {
 975                                 payee: Some(params.payee.clone()), ..Self::route_for_value(params.final_value_msat)
 976                         })
 977                 }
 978         }
 979
 980         struct FailingRouter;
 981
 982         impl<S: routing::Score> Router<S> for FailingRouter {
 983                 fn find_route(
 984                         &self,
 985                         _payer: &PublicKey,
 986                         _params: &RouteParameters,
 987                         _first_hops: Option<&[&ChannelDetails]>,
 988                         _scorer: &S,
 989                 ) -> Result<Route, LightningError> {
 990                         Err(LightningError { err: String::new(), action: ErrorAction::IgnoreError })
 991                 }
 992         }
 993
 994         struct TestScorer {
 995                 expectations: std::collections::VecDeque<u64>,
 996         }
 997
 998         impl TestScorer {
 999                 fn new() -> Self {
1000                         Self {
1001                                 expectations: std::collections::VecDeque::new(),
1002                         }
1003                 }
1004
1005                 fn expect_channel_failure(mut self, short_channel_id: u64) -> Self {
1006                         self.expectations.push_back(short_channel_id);
1007                         self
1008                 }
1009         }
1010
1011         impl routing::Score for TestScorer {
1012                 fn channel_penalty_msat(
1013                         &self, _short_channel_id: u64, _source: &NodeId, _target: &NodeId
1014                 ) -> u64 { 0 }
1015
1016                 fn payment_path_failed(&mut self, _path: &Vec<RouteHop>, short_channel_id: u64) {
1017                         if let Some(expected_short_channel_id) = self.expectations.pop_front() {
1018                                 assert_eq!(short_channel_id, expected_short_channel_id);
1019                         }
1020                 }
1021         }
1022
1023         impl Drop for TestScorer {
1024                 fn drop(&mut self) {
1025                         if std::thread::panicking() {
1026                                 return;
1027                         }
1028
1029                         if !self.expectations.is_empty() {
1030                                 panic!("Unsatisfied channel failure expectations: {:?}", self.expectations);
1031                         }
1032                 }
1033         }
1034
1035         struct TestPayer {
1036                 expectations: core::cell::RefCell<std::collections::VecDeque<u64>>,
1037                 attempts: core::cell::RefCell<usize>,
1038                 failing_on_attempt: Option<usize>,
1039         }
1040
1041         impl TestPayer {
1042                 fn new() -> Self {
1043                         Self {
1044                                 expectations: core::cell::RefCell::new(std::collections::VecDeque::new()),
1045                                 attempts: core::cell::RefCell::new(0),
1046                                 failing_on_attempt: None,
1047                         }
1048                 }
1049
1050                 fn expect_value_msat(self, value_msat: u64) -> Self {
1051                         self.expectations.borrow_mut().push_back(value_msat);
1052                         self
1053                 }
1054
1055                 fn fails_on_attempt(self, attempt: usize) -> Self {
1056                         Self {
1057                                 expectations: core::cell::RefCell::new(self.expectations.borrow().clone()),
1058                                 attempts: core::cell::RefCell::new(0),
1059                                 failing_on_attempt: Some(attempt),
1060                         }
1061                 }
1062
1063                 fn check_attempts(&self) -> bool {
1064                         let mut attempts = self.attempts.borrow_mut();
1065                         *attempts += 1;
1066                         match self.failing_on_attempt {
1067                                 None => true,
1068                                 Some(attempt) if attempt != *attempts => true,
1069                                 Some(_) => false,
1070                         }
1071                 }
1072
1073                 fn check_value_msats(&self, route: &Route) {
1074                         let expected_value_msats = self.expectations.borrow_mut().pop_front();
1075                         if let Some(expected_value_msats) = expected_value_msats {
1076                                 let actual_value_msats = route.get_total_amount();
1077                                 assert_eq!(actual_value_msats, expected_value_msats);
1078                         }
1079                 }
1080         }
1081
1082         impl Drop for TestPayer {
1083                 fn drop(&mut self) {
1084                         if std::thread::panicking() {
1085                                 return;
1086                         }
1087
1088                         if !self.expectations.borrow().is_empty() {
1089                                 panic!("Unsatisfied payment expectations: {:?}", self.expectations.borrow());
1090                         }
1091                 }
1092         }
1093
1094         impl Payer for TestPayer {
1095                 fn node_id(&self) -> PublicKey {
1096                         let secp_ctx = Secp256k1::new();
1097                         PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32]).unwrap())
1098                 }
1099
1100                 fn first_hops(&self) -> Vec<ChannelDetails> {
1101                         Vec::new()
1102                 }
1103
1104                 fn send_payment(
1105                         &self,
1106                         route: &Route,
1107                         _payment_hash: PaymentHash,
1108                         _payment_secret: &Option<PaymentSecret>
1109                 ) -> Result<PaymentId, PaymentSendFailure> {
1110                         if self.check_attempts() {
1111                                 self.check_value_msats(route);
1112                                 Ok(PaymentId([1; 32]))
1113                         } else {
1114                                 Err(PaymentSendFailure::ParameterError(APIError::MonitorUpdateFailed))
1115                         }
1116                 }
1117
1118                 fn retry_payment(
1119                         &self, route: &Route, _payment_id: PaymentId
1120                 ) -> Result<(), PaymentSendFailure> {
1121                         if self.check_attempts() {
1122                                 self.check_value_msats(route);
1123                                 Ok(())
1124                         } else {
1125                                 Err(PaymentSendFailure::ParameterError(APIError::MonitorUpdateFailed))
1126                         }
1127                 }
1128         }
1129 }