Merge pull request #1806 from arik-so/2022-10-background-processor-deparametrization
[rust-lightning] / lightning-invoice / src / payment.rs
index a97bf2fced407303619b5f136f11d13a5f0c1f59..cbd760c37d02d045c82cbc942432c1f2c82dc419 100644 (file)
 //! and payee using information provided by the payer and from the payee's [`Invoice`], when
 //! applicable.
 //!
-//! [`InvoicePayer`] is parameterized by a [`LockableScore`], which it uses for scoring failed and
-//! successful payment paths upon receiving [`Event::PaymentPathFailed`] and
-//! [`Event::PaymentPathSuccessful`] events, respectively.
+//! [`InvoicePayer`] uses its [`Router`] parameterization for optionally notifying scorers upon
+//! receiving the [`Event::PaymentPathFailed`] and [`Event::PaymentPathSuccessful`] events.
+//! It also does the same for payment probe failure and success events using [`Event::ProbeFailed`]
+//! and [`Event::ProbeSuccessful`].
 //!
 //! [`InvoicePayer`] is capable of retrying failed payments. It accomplishes this by implementing
 //! [`EventHandler`] which decorates a user-provided handler. It will intercept any
 //! # extern crate lightning_invoice;
 //! # extern crate secp256k1;
 //! #
-//! # #[cfg(feature = "no-std")]
-//! # extern crate core2;
-//! #
+//! # use lightning::io;
 //! # use lightning::ln::{PaymentHash, PaymentPreimage, PaymentSecret};
 //! # use lightning::ln::channelmanager::{ChannelDetails, PaymentId, PaymentSendFailure};
 //! # use lightning::ln::msgs::LightningError;
 //! # use lightning::routing::gossip::NodeId;
-//! # use lightning::routing::router::{Route, RouteHop, RouteParameters};
+//! # use lightning::routing::router::{InFlightHtlcs, Route, RouteHop, RouteParameters, Router};
 //! # use lightning::routing::scoring::{ChannelUsage, Score};
 //! # use lightning::util::events::{Event, EventHandler, EventsProvider};
 //! # use lightning::util::logger::{Logger, Record};
 //! # use lightning::util::ser::{Writeable, Writer};
 //! # use lightning_invoice::Invoice;
-//! # use lightning_invoice::payment::{InvoicePayer, Payer, Retry, Router};
+//! # use lightning_invoice::payment::{InvoicePayer, Payer, Retry, ScoringRouter};
 //! # use secp256k1::PublicKey;
 //! # use std::cell::RefCell;
 //! # use std::ops::Deref;
 //! #
-//! # #[cfg(not(feature = "std"))]
-//! # use core2::io;
-//! # #[cfg(feature = "std")]
-//! # use std::io;
-//! #
 //! # struct FakeEventProvider {}
 //! # impl EventsProvider for FakeEventProvider {
 //! #     fn process_pending_events<H: Deref>(&self, handler: H) where H::Target: EventHandler {}
 //! #     fn node_id(&self) -> PublicKey { unimplemented!() }
 //! #     fn first_hops(&self) -> Vec<ChannelDetails> { unimplemented!() }
 //! #     fn send_payment(
-//! #         &self, route: &Route, payment_hash: PaymentHash, payment_secret: &Option<PaymentSecret>
-//! #     ) -> Result<PaymentId, PaymentSendFailure> { unimplemented!() }
+//! #         &self, route: &Route, payment_hash: PaymentHash, payment_secret: &Option<PaymentSecret>,
+//! #         payment_id: PaymentId
+//! #     ) -> Result<(), PaymentSendFailure> { unimplemented!() }
 //! #     fn send_spontaneous_payment(
-//! #         &self, route: &Route, payment_preimage: PaymentPreimage
-//! #     ) -> Result<PaymentId, PaymentSendFailure> { unimplemented!() }
+//! #         &self, route: &Route, payment_preimage: PaymentPreimage, payment_id: PaymentId,
+//! #     ) -> Result<(), PaymentSendFailure> { unimplemented!() }
 //! #     fn retry_payment(
 //! #         &self, route: &Route, payment_id: PaymentId
 //! #     ) -> Result<(), PaymentSendFailure> { unimplemented!() }
 //! #
 //! # struct FakeRouter {}
 //! # impl Router for FakeRouter {
-//! #     fn find_route<S: Score>(
-//! #         &self, payer: &PublicKey, params: &RouteParameters, payment_hash: &PaymentHash,
-//! #         first_hops: Option<&[&ChannelDetails]>, scorer: &S
+//! #     fn find_route(
+//! #         &self, payer: &PublicKey, params: &RouteParameters,
+//! #         first_hops: Option<&[&ChannelDetails]>, _inflight_htlcs: InFlightHtlcs
 //! #     ) -> Result<Route, LightningError> { unimplemented!() }
 //! # }
+//! # impl ScoringRouter for FakeRouter {
+//! #     fn notify_payment_path_failed(&self, path: &[&RouteHop], short_channel_id: u64) {  unimplemented!() }
+//! #     fn notify_payment_path_successful(&self, path: &[&RouteHop]) {  unimplemented!() }
+//! #     fn notify_payment_probe_successful(&self, path: &[&RouteHop]) {  unimplemented!() }
+//! #     fn notify_payment_probe_failed(&self, path: &[&RouteHop], short_channel_id: u64) { unimplemented!() }
+//! # }
 //! #
 //! # struct FakeScorer {}
 //! # impl Writeable for FakeScorer {
 //! # }
 //! #
 //! # fn main() {
-//! let event_handler = |event: &Event| {
+//! let event_handler = |event: Event| {
 //!     match event {
 //!         Event::PaymentPathFailed { .. } => println!("payment failed after retries"),
 //!         Event::PaymentSent { .. } => println!("payment successful"),
 //! # let router = FakeRouter {};
 //! # let scorer = RefCell::new(FakeScorer {});
 //! # let logger = FakeLogger {};
-//! let invoice_payer = InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+//! let invoice_payer = InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 //!
 //! let invoice = "...";
 //! if let Ok(invoice) = invoice.parse::<Invoice>() {
@@ -145,18 +146,18 @@ use lightning::ln::{PaymentHash, PaymentPreimage, PaymentSecret};
 use lightning::ln::channelmanager::{ChannelDetails, PaymentId, PaymentSendFailure};
 use lightning::ln::msgs::LightningError;
 use lightning::routing::gossip::NodeId;
-use lightning::routing::scoring::{ChannelUsage, LockableScore, Score};
-use lightning::routing::router::{PaymentParameters, Route, RouteHop, RouteParameters};
+use lightning::routing::router::{InFlightHtlcs, PaymentParameters, Route, RouteHop, RouteParameters, Router};
 use lightning::util::errors::APIError;
 use lightning::util::events::{Event, EventHandler};
 use lightning::util::logger::Logger;
-use time_utils::Time;
+use crate::time_utils::Time;
 use crate::sync::Mutex;
 
 use secp256k1::PublicKey;
 
 use core::fmt;
 use core::fmt::{Debug, Display, Formatter};
+use core::future::Future;
 use core::ops::Deref;
 use core::time::Duration;
 #[cfg(feature = "std")]
@@ -167,25 +168,35 @@ use std::time::SystemTime;
 /// See [module-level documentation] for details.
 ///
 /// [module-level documentation]: crate::payment
-pub type InvoicePayer<P, R, S, L, E> = InvoicePayerUsingTime::<P, R, S, L, E, ConfiguredTime>;
+pub type InvoicePayer<P, R, L, E> = InvoicePayerUsingTime::<P, R, L, E, ConfiguredTime>;
 
 #[cfg(not(feature = "no-std"))]
 type ConfiguredTime = std::time::Instant;
 #[cfg(feature = "no-std")]
-use time_utils;
+use crate::time_utils;
 #[cfg(feature = "no-std")]
 type ConfiguredTime = time_utils::Eternity;
 
+/// Sealed trait with a blanket implementation to allow both sync and async implementations of event
+/// handling to exist within the InvoicePayer.
+mod sealed {
+       pub trait BaseEventHandler {}
+       impl<T> BaseEventHandler for T {}
+}
+
 /// (C-not exported) generally all users should use the [`InvoicePayer`] type alias.
-pub struct InvoicePayerUsingTime<P: Deref, R: Router, S: Deref, L: Deref, E: EventHandler, T: Time>
-where
+pub struct InvoicePayerUsingTime<
+       P: Deref,
+       R: ScoringRouter,
+       L: Deref,
+       E: sealed::BaseEventHandler,
+       T: Time
+> where
        P::Target: Payer,
-       S::Target: for <'a> LockableScore<'a>,
        L::Target: Logger,
 {
        payer: P,
        router: R,
-       scorer: S,
        logger: L,
        event_handler: E,
        /// Caches the overall attempts at making a payment, which is updated prior to retrying.
@@ -209,49 +220,6 @@ impl<T: Time> PaymentInfo<T> {
        }
 }
 
-/// Used to store information about all the HTLCs that are inflight across all payment attempts
-struct AccountForInFlightHtlcs<'a, S: Score> {
-       scorer: &'a mut S,
-       /// Maps a channel's short channel id and its direction to the liquidity used up.
-       inflight_htlcs: HashMap<(u64, bool), u64>,
-}
-
-#[cfg(c_bindings)]
-impl<'a, S:Score> lightning::util::ser::Writeable for AccountForInFlightHtlcs<'a, S> {
-       fn write<W: lightning::util::ser::Writer>(&self, writer: &mut W) -> Result<(), std::io::Error> { self.scorer.write(writer) }
-}
-
-impl<'a, S: Score> Score for AccountForInFlightHtlcs<'a, S> {
-       fn channel_penalty_msat(&self, short_channel_id: u64, source: &NodeId, target: &NodeId, usage: ChannelUsage) -> u64 {
-               if let Some(used_liqudity) = self.inflight_htlcs.get(&(short_channel_id, source < target)) {
-                       let usage = ChannelUsage {
-                               inflight_htlc_msat: usage.inflight_htlc_msat + used_liqudity,
-                               ..usage
-                       };
-
-                       self.scorer.channel_penalty_msat(short_channel_id, source, target, usage)
-               } else {
-                       self.scorer.channel_penalty_msat(short_channel_id, source, target, usage)
-               }
-       }
-
-       fn payment_path_failed(&mut self, path: &[&RouteHop], short_channel_id: u64) {
-               self.scorer.payment_path_failed(path, short_channel_id)
-       }
-
-       fn payment_path_successful(&mut self, path: &[&RouteHop]) {
-               self.scorer.payment_path_successful(path)
-       }
-
-       fn probe_failed(&mut self, path: &[&RouteHop], short_channel_id: u64) {
-               self.scorer.probe_failed(path, short_channel_id)
-       }
-
-       fn probe_successful(&mut self, path: &[&RouteHop]) {
-               self.scorer.probe_successful(path)
-       }
-}
-
 /// Storing minimal payment attempts information required for determining if a outbound payment can
 /// be retried.
 #[derive(Clone, Copy)]
@@ -287,6 +255,18 @@ impl<T: Time> Display for PaymentAttempts<T> {
 }
 
 /// A trait defining behavior of an [`Invoice`] payer.
+///
+/// While the behavior of [`InvoicePayer`] provides idempotency of duplicate `send_*payment` calls
+/// with the same [`PaymentHash`], it is up to the `Payer` to provide idempotency across restarts.
+///
+/// [`ChannelManager`] provides idempotency for duplicate payments with the same [`PaymentId`].
+///
+/// In order to trivially ensure idempotency for payments, the default `Payer` implementation
+/// reuses the [`PaymentHash`] bytes as the [`PaymentId`]. Custom implementations wishing to
+/// provide payment idempotency with a different idempotency key (i.e. [`PaymentId`]) should map
+/// the [`Invoice`] or spontaneous payment target pubkey to their own idempotency key.
+///
+/// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
 pub trait Payer {
        /// Returns the payer's node id.
        fn node_id(&self) -> PublicKey;
@@ -296,13 +276,14 @@ pub trait Payer {
 
        /// Sends a payment over the Lightning Network using the given [`Route`].
        fn send_payment(
-               &self, route: &Route, payment_hash: PaymentHash, payment_secret: &Option<PaymentSecret>
-       ) -> Result<PaymentId, PaymentSendFailure>;
+               &self, route: &Route, payment_hash: PaymentHash, payment_secret: &Option<PaymentSecret>,
+               payment_id: PaymentId
+       ) -> Result<(), PaymentSendFailure>;
 
        /// Sends a spontaneous payment over the Lightning Network using the given [`Route`].
        fn send_spontaneous_payment(
-               &self, route: &Route, payment_preimage: PaymentPreimage
-       ) -> Result<PaymentId, PaymentSendFailure>;
+               &self, route: &Route, payment_preimage: PaymentPreimage, payment_id: PaymentId
+       ) -> Result<(), PaymentSendFailure>;
 
        /// Retries a failed payment path for the [`PaymentId`] using the given [`Route`].
        fn retry_payment(&self, route: &Route, payment_id: PaymentId) -> Result<(), PaymentSendFailure>;
@@ -311,13 +292,28 @@ pub trait Payer {
        fn abandon_payment(&self, payment_id: PaymentId);
 }
 
-/// A trait defining behavior for routing an [`Invoice`] payment.
-pub trait Router {
-       /// Finds a [`Route`] between `payer` and `payee` for a payment with the given values.
-       fn find_route<S: Score>(
-               &self, payer: &PublicKey, route_params: &RouteParameters, payment_hash: &PaymentHash,
-               first_hops: Option<&[&ChannelDetails]>, scorer: &S
-       ) -> Result<Route, LightningError>;
+/// A trait defining behavior for a [`Router`] implementation that also supports scoring channels
+/// based on payment and probe success/failure.
+///
+/// [`Router`]: lightning::routing::router::Router
+pub trait ScoringRouter: Router {
+       /// Finds a [`Route`] between `payer` and `payee` for a payment with the given values. Includes
+       /// `PaymentHash` and `PaymentId` to be able to correlate the request with a specific payment.
+       fn find_route_with_id(
+               &self, payer: &PublicKey, route_params: &RouteParameters,
+               first_hops: Option<&[&ChannelDetails]>, inflight_htlcs: InFlightHtlcs,
+               _payment_hash: PaymentHash, _payment_id: PaymentId
+       ) -> Result<Route, LightningError> {
+               self.find_route(payer, route_params, first_hops, inflight_htlcs)
+       }
+       /// Lets the router know that payment through a specific path has failed.
+       fn notify_payment_path_failed(&self, path: &[&RouteHop], short_channel_id: u64);
+       /// Lets the router know that payment through a specific path was successful.
+       fn notify_payment_path_successful(&self, path: &[&RouteHop]);
+       /// Lets the router know that a payment probe was successful.
+       fn notify_payment_probe_successful(&self, path: &[&RouteHop]);
+       /// Lets the router know that a payment probe failed.
+       fn notify_payment_probe_failed(&self, path: &[&RouteHop], short_channel_id: u64);
 }
 
 /// Strategies available to retry payment path failures for an [`Invoice`].
@@ -359,10 +355,10 @@ pub enum PaymentError {
        Sending(PaymentSendFailure),
 }
 
-impl<P: Deref, R: Router, S: Deref, L: Deref, E: EventHandler, T: Time> InvoicePayerUsingTime<P, R, S, L, E, T>
+impl<P: Deref, R: ScoringRouter, L: Deref, E: sealed::BaseEventHandler, T: Time>
+       InvoicePayerUsingTime<P, R, L, E, T>
 where
        P::Target: Payer,
-       S::Target: for <'a> LockableScore<'a>,
        L::Target: Logger,
 {
        /// Creates an invoice payer that retries failed payment paths.
@@ -370,12 +366,11 @@ where
        /// Will forward any [`Event::PaymentPathFailed`] events to the decorated `event_handler` once
        /// `retry` has been exceeded for a given [`Invoice`].
        pub fn new(
-               payer: P, router: R, scorer: S, logger: L, event_handler: E, retry: Retry
+               payer: P, router: R, logger: L, event_handler: E, retry: Retry
        ) -> Self {
                Self {
                        payer,
                        router,
-                       scorer,
                        logger,
                        event_handler,
                        payment_cache: Mutex::new(HashMap::new()),
@@ -385,36 +380,76 @@ where
 
        /// Pays the given [`Invoice`], caching it for later use in case a retry is needed.
        ///
-       /// You should ensure that the `invoice.payment_hash()` is unique and the same payment_hash has
-       /// never been paid before. Because [`InvoicePayer`] is stateless no effort is made to do so
-       /// for you.
+       /// [`Invoice::payment_hash`] is used as the [`PaymentId`], which ensures idempotency as long
+       /// as the payment is still pending. Once the payment completes or fails, you must ensure that
+       /// a second payment with the same [`PaymentHash`] is never sent.
+       ///
+       /// If you wish to use a different payment idempotency token, see
+       /// [`Self::pay_invoice_with_id`].
        pub fn pay_invoice(&self, invoice: &Invoice) -> Result<PaymentId, PaymentError> {
+               let payment_id = PaymentId(invoice.payment_hash().into_inner());
+               self.pay_invoice_with_id(invoice, payment_id).map(|()| payment_id)
+       }
+
+       /// Pays the given [`Invoice`] with a custom idempotency key, caching the invoice for later use
+       /// in case a retry is needed.
+       ///
+       /// Note that idempotency is only guaranteed as long as the payment is still pending. Once the
+       /// payment completes or fails, no idempotency guarantees are made.
+       ///
+       /// You should ensure that the [`Invoice::payment_hash`] is unique and the same [`PaymentHash`]
+       /// has never been paid before.
+       ///
+       /// See [`Self::pay_invoice`] for a variant which uses the [`PaymentHash`] for the idempotency
+       /// token.
+       pub fn pay_invoice_with_id(&self, invoice: &Invoice, payment_id: PaymentId) -> Result<(), PaymentError> {
                if invoice.amount_milli_satoshis().is_none() {
                        Err(PaymentError::Invoice("amount missing"))
                } else {
-                       self.pay_invoice_using_amount(invoice, None)
+                       self.pay_invoice_using_amount(invoice, None, payment_id)
                }
        }
 
        /// Pays the given zero-value [`Invoice`] using the given amount, caching it for later use in
        /// case a retry is needed.
        ///
-       /// You should ensure that the `invoice.payment_hash()` is unique and the same payment_hash has
-       /// never been paid before. Because [`InvoicePayer`] is stateless no effort is made to do so
-       /// for you.
+       /// [`Invoice::payment_hash`] is used as the [`PaymentId`], which ensures idempotency as long
+       /// as the payment is still pending. Once the payment completes or fails, you must ensure that
+       /// a second payment with the same [`PaymentHash`] is never sent.
+       ///
+       /// If you wish to use a different payment idempotency token, see
+       /// [`Self::pay_zero_value_invoice_with_id`].
        pub fn pay_zero_value_invoice(
                &self, invoice: &Invoice, amount_msats: u64
        ) -> Result<PaymentId, PaymentError> {
+               let payment_id = PaymentId(invoice.payment_hash().into_inner());
+               self.pay_zero_value_invoice_with_id(invoice, amount_msats, payment_id).map(|()| payment_id)
+       }
+
+       /// Pays the given zero-value [`Invoice`] using the given amount and custom idempotency key,
+       /// caching the invoice for later use in case a retry is needed.
+       ///
+       /// Note that idempotency is only guaranteed as long as the payment is still pending. Once the
+       /// payment completes or fails, no idempotency guarantees are made.
+       ///
+       /// You should ensure that the [`Invoice::payment_hash`] is unique and the same [`PaymentHash`]
+       /// has never been paid before.
+       ///
+       /// See [`Self::pay_zero_value_invoice`] for a variant which uses the [`PaymentHash`] for the
+       /// idempotency token.
+       pub fn pay_zero_value_invoice_with_id(
+               &self, invoice: &Invoice, amount_msats: u64, payment_id: PaymentId
+       ) -> Result<(), PaymentError> {
                if invoice.amount_milli_satoshis().is_some() {
                        Err(PaymentError::Invoice("amount unexpected"))
                } else {
-                       self.pay_invoice_using_amount(invoice, Some(amount_msats))
+                       self.pay_invoice_using_amount(invoice, Some(amount_msats), payment_id)
                }
        }
 
        fn pay_invoice_using_amount(
-               &self, invoice: &Invoice, amount_msats: Option<u64>
-       ) -> Result<PaymentId, PaymentError> {
+               &self, invoice: &Invoice, amount_msats: Option<u64>, payment_id: PaymentId
+       ) -> Result<(), PaymentError> {
                debug_assert!(invoice.amount_milli_satoshis().is_some() ^ amount_msats.is_some());
 
                let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
@@ -437,7 +472,7 @@ where
                };
 
                let send_payment = |route: &Route| {
-                       self.payer.send_payment(route, payment_hash, &payment_secret)
+                       self.payer.send_payment(route, payment_hash, &payment_secret, payment_id)
                };
 
                self.pay_internal(&route_params, payment_hash, send_payment)
@@ -447,13 +482,41 @@ where
        /// Pays `pubkey` an amount using the hash of the given preimage, caching it for later use in
        /// case a retry is needed.
        ///
-       /// You should ensure that `payment_preimage` is unique and that its `payment_hash` has never
-       /// been paid before. Because [`InvoicePayer`] is stateless no effort is made to do so for you.
+       /// The hash of the [`PaymentPreimage`] is used as the [`PaymentId`], which ensures idempotency
+       /// as long as the payment is still pending. Once the payment completes or fails, you must
+       /// ensure that a second payment with the same [`PaymentPreimage`] is never sent.
        pub fn pay_pubkey(
                &self, pubkey: PublicKey, payment_preimage: PaymentPreimage, amount_msats: u64,
                final_cltv_expiry_delta: u32
        ) -> Result<PaymentId, PaymentError> {
                let payment_hash = PaymentHash(Sha256::hash(&payment_preimage.0).into_inner());
+               let payment_id = PaymentId(payment_hash.0);
+               self.do_pay_pubkey(pubkey, payment_preimage, payment_hash, payment_id, amount_msats,
+                               final_cltv_expiry_delta)
+                       .map(|()| payment_id)
+       }
+
+       /// Pays `pubkey` an amount using the hash of the given preimage and a custom idempotency key,
+       /// caching the invoice for later use in case a retry is needed.
+       ///
+       /// Note that idempotency is only guaranteed as long as the payment is still pending. Once the
+       /// payment completes or fails, no idempotency guarantees are made.
+       ///
+       /// You should ensure that the [`PaymentPreimage`] is unique and the corresponding
+       /// [`PaymentHash`] has never been paid before.
+       pub fn pay_pubkey_with_id(
+               &self, pubkey: PublicKey, payment_preimage: PaymentPreimage, payment_id: PaymentId,
+               amount_msats: u64, final_cltv_expiry_delta: u32
+       ) -> Result<(), PaymentError> {
+               let payment_hash = PaymentHash(Sha256::hash(&payment_preimage.0).into_inner());
+               self.do_pay_pubkey(pubkey, payment_preimage, payment_hash, payment_id, amount_msats,
+                               final_cltv_expiry_delta)
+       }
+
+       fn do_pay_pubkey(
+               &self, pubkey: PublicKey, payment_preimage: PaymentPreimage, payment_hash: PaymentHash,
+               payment_id: PaymentId, amount_msats: u64, final_cltv_expiry_delta: u32
+       ) -> Result<(), PaymentError> {
                match self.payment_cache.lock().unwrap().entry(payment_hash) {
                        hash_map::Entry::Occupied(_) => return Err(PaymentError::Invoice("payment pending")),
                        hash_map::Entry::Vacant(entry) => entry.insert(PaymentInfo::new()),
@@ -466,15 +529,15 @@ where
                };
 
                let send_payment = |route: &Route| {
-                       self.payer.send_spontaneous_payment(route, payment_preimage)
+                       self.payer.send_spontaneous_payment(route, payment_preimage, payment_id)
                };
                self.pay_internal(&route_params, payment_hash, send_payment)
                        .map_err(|e| { self.payment_cache.lock().unwrap().remove(&payment_hash); e })
        }
 
-       fn pay_internal<F: FnOnce(&Route) -> Result<PaymentId, PaymentSendFailure> + Copy>(
+       fn pay_internal<F: FnOnce(&Route) -> Result<(), PaymentSendFailure> + Copy>(
                &self, params: &RouteParameters, payment_hash: PaymentHash, send_payment: F,
-       ) -> Result<PaymentId, PaymentError> {
+       ) -> Result<(), PaymentError> {
                #[cfg(feature = "std")] {
                        if has_expired(params) {
                                log_trace!(self.logger, "Invoice expired prior to send for payment {}", log_bytes!(payment_hash.0));
@@ -486,16 +549,15 @@ where
                let first_hops = self.payer.first_hops();
                let inflight_htlcs = self.create_inflight_map();
                let route = self.router.find_route(
-                       &payer, &params, &payment_hash, Some(&first_hops.iter().collect::<Vec<_>>()),
-                       &AccountForInFlightHtlcs { scorer: &mut self.scorer.lock(), inflight_htlcs }
+                       &payer, &params, Some(&first_hops.iter().collect::<Vec<_>>()), inflight_htlcs
                ).map_err(|e| PaymentError::Routing(e))?;
 
                match send_payment(&route) {
-                       Ok(payment_id) => {
+                       Ok(()) => {
                                for path in route.paths {
                                        self.process_path_inflight_htlcs(payment_hash, path);
                                }
-                               Ok(payment_id)
+                               Ok(())
                        },
                        Err(e) => match e {
                                PaymentSendFailure::ParameterError(_) => Err(e),
@@ -513,11 +575,11 @@ where
                                },
                                PaymentSendFailure::PartialFailure { failed_paths_retry, payment_id, results } => {
                                        // If a `PartialFailure` event returns a result that is an `Ok()`, it means that
-                                       // part of our payment is retried. When we receive `MonitorUpdateFailed`, it
+                                       // part of our payment is retried. When we receive `MonitorUpdateInProgress`, it
                                        // means that we are still waiting for our channel monitor update to be completed.
                                        for (result, path) in results.iter().zip(route.paths.into_iter()) {
                                                match result {
-                                                       Ok(_) | Err(APIError::MonitorUpdateFailed) => {
+                                                       Ok(_) | Err(APIError::MonitorUpdateInProgress) => {
                                                                self.process_path_inflight_htlcs(payment_hash, path);
                                                        },
                                                        _ => {},
@@ -530,13 +592,13 @@ where
                                                // consider the payment sent, so return `Ok()` here, ignoring any retry
                                                // errors.
                                                let _ = self.retry_payment(payment_id, payment_hash, &retry_data);
-                                               Ok(payment_id)
+                                               Ok(())
                                        } else {
                                                // This may happen if we send a payment and some paths fail, but
                                                // only due to a temporary monitor failure or the like, implying
                                                // they're really in-flight, but we haven't sent the initial
                                                // HTLC-Add messages yet.
-                                               Ok(payment_id)
+                                               Ok(())
                                        }
                                },
                        },
@@ -591,8 +653,7 @@ where
                let inflight_htlcs = self.create_inflight_map();
 
                let route = self.router.find_route(
-                       &payer, &params, &payment_hash, Some(&first_hops.iter().collect::<Vec<_>>()),
-                       &AccountForInFlightHtlcs { scorer: &mut self.scorer.lock(), inflight_htlcs }
+                       &payer, &params, Some(&first_hops.iter().collect::<Vec<_>>()), inflight_htlcs
                );
 
                if route.is_err() {
@@ -617,11 +678,11 @@ where
                        },
                        Err(PaymentSendFailure::PartialFailure { failed_paths_retry, results, .. }) => {
                                // If a `PartialFailure` error contains a result that is an `Ok()`, it means that
-                               // part of our payment is retried. When we receive `MonitorUpdateFailed`, it
+                               // part of our payment is retried. When we receive `MonitorUpdateInProgress`, it
                                // means that we are still waiting for our channel monitor update to complete.
                                for (result, path) in results.iter().zip(route.unwrap().paths.into_iter()) {
                                        match result {
-                                               Ok(_) | Err(APIError::MonitorUpdateFailed) => {
+                                               Ok(_) | Err(APIError::MonitorUpdateInProgress) => {
                                                        self.process_path_inflight_htlcs(payment_hash, path);
                                                },
                                                _ => {},
@@ -645,13 +706,12 @@ where
                self.payment_cache.lock().unwrap().remove(payment_hash);
        }
 
-       /// Given a [`PaymentHash`], this function looks up inflight path attempts in the payment_cache.
-       /// Then, it uses the path information inside the cache to construct a HashMap mapping a channel's
-       /// short channel id and direction to the amount being sent through it.
+       /// Use path information in the payment_cache to construct a HashMap mapping a channel's short
+       /// channel id and direction to the amount being sent through it.
        ///
        /// This function should be called whenever we need information about currently used up liquidity
        /// across payments.
-       fn create_inflight_map(&self) -> HashMap<(u64, bool), u64> {
+       fn create_inflight_map(&self) -> InFlightHtlcs {
                let mut total_inflight_map: HashMap<(u64, bool), u64> = HashMap::new();
                // Make an attempt at finding existing payment information from `payment_cache`. If it
                // does not exist, it probably is a fresh payment and we can just return an empty
@@ -683,7 +743,7 @@ where
                        }
                }
 
-               total_inflight_map
+               InFlightHtlcs::new(total_inflight_map)
        }
 }
 
@@ -698,13 +758,15 @@ fn has_expired(route_params: &RouteParameters) -> bool {
        } else { false }
 }
 
-impl<P: Deref, R: Router, S: Deref, L: Deref, E: EventHandler, T: Time> EventHandler for InvoicePayerUsingTime<P, R, S, L, E, T>
+impl<P: Deref, R: ScoringRouter, L: Deref, E: sealed::BaseEventHandler, T: Time>
+       InvoicePayerUsingTime<P, R, L, E, T>
 where
        P::Target: Payer,
-       S::Target: for <'a> LockableScore<'a>,
        L::Target: Logger,
 {
-       fn handle_event(&self, event: &Event) {
+       /// Returns a bool indicating whether the processed event should be forwarded to a user-provided
+       /// event handler.
+       fn handle_event_internal(&self, event: &Event) -> bool {
                match event {
                        Event::PaymentPathFailed { payment_hash, path, ..  }
                        | Event::PaymentPathSuccessful { path, payment_hash: Some(payment_hash), .. }
@@ -721,7 +783,7 @@ where
                        } => {
                                if let Some(short_channel_id) = short_channel_id {
                                        let path = path.iter().collect::<Vec<_>>();
-                                       self.scorer.lock().payment_path_failed(&path, *short_channel_id);
+                                       self.router.notify_payment_path_failed(&path, *short_channel_id)
                                }
 
                                if payment_id.is_none() {
@@ -734,7 +796,7 @@ where
                                        self.payer.abandon_payment(payment_id.unwrap());
                                } else if self.retry_payment(payment_id.unwrap(), *payment_hash, retry.as_ref().unwrap()).is_ok() {
                                        // We retried at least somewhat, don't provide the PaymentPathFailed event to the user.
-                                       return;
+                                       return false;
                                } else {
                                        self.payer.abandon_payment(payment_id.unwrap());
                                }
@@ -744,7 +806,7 @@ where
                        },
                        Event::PaymentPathSuccessful { path, .. } => {
                                let path = path.iter().collect::<Vec<_>>();
-                               self.scorer.lock().payment_path_successful(&path);
+                               self.router.notify_payment_path_successful(&path);
                        },
                        Event::PaymentSent { payment_hash, .. } => {
                                let mut payment_cache = self.payment_cache.lock().unwrap();
@@ -756,20 +818,50 @@ where
                        Event::ProbeSuccessful { payment_hash, path, .. } => {
                                log_trace!(self.logger, "Probe payment {} of {}msat was successful", log_bytes!(payment_hash.0), path.last().unwrap().fee_msat);
                                let path = path.iter().collect::<Vec<_>>();
-                               self.scorer.lock().probe_successful(&path);
+                               self.router.notify_payment_probe_successful(&path);
                        },
                        Event::ProbeFailed { payment_hash, path, short_channel_id, .. } => {
                                if let Some(short_channel_id) = short_channel_id {
                                        log_trace!(self.logger, "Probe payment {} of {}msat failed at channel {}", log_bytes!(payment_hash.0), path.last().unwrap().fee_msat, *short_channel_id);
                                        let path = path.iter().collect::<Vec<_>>();
-                                       self.scorer.lock().probe_failed(&path, *short_channel_id);
+                                       self.router.notify_payment_probe_failed(&path, *short_channel_id);
                                }
                        },
                        _ => {},
                }
 
                // Delegate to the decorated event handler unless the payment is retried.
-               self.event_handler.handle_event(event)
+               true
+       }
+}
+
+impl<P: Deref, R: ScoringRouter, L: Deref, E: EventHandler, T: Time>
+       EventHandler for InvoicePayerUsingTime<P, R, L, E, T>
+where
+       P::Target: Payer,
+       L::Target: Logger,
+{
+       fn handle_event(&self, event: Event) {
+               let should_forward = self.handle_event_internal(&event);
+               if should_forward {
+                       self.event_handler.handle_event(event)
+               }
+       }
+}
+
+impl<P: Deref, R: ScoringRouter, L: Deref, T: Time, F: Future, H: Fn(Event) -> F>
+       InvoicePayerUsingTime<P, R, L, H, T>
+where
+       P::Target: Payer,
+       L::Target: Logger,
+{
+       /// Intercepts events required by the [`InvoicePayer`] and forwards them to the underlying event
+       /// handler, if necessary, to handle them asynchronously.
+       pub async fn handle_event_async(&self, event: Event) {
+               let should_forward = self.handle_event_internal(&event);
+               if should_forward {
+                       (self.event_handler)(event).await;
+               }
        }
 }
 
@@ -777,25 +869,27 @@ where
 mod tests {
        use super::*;
        use crate::{InvoiceBuilder, Currency};
-       use utils::create_invoice_from_channelmanager_and_duration_since_epoch;
+       use crate::utils::{ScorerAccountingForInFlightHtlcs, create_invoice_from_channelmanager_and_duration_since_epoch};
        use bitcoin_hashes::sha256::Hash as Sha256;
        use lightning::ln::PaymentPreimage;
-       use lightning::ln::features::{ChannelFeatures, NodeFeatures, InitFeatures};
+       use lightning::ln::channelmanager;
+       use lightning::ln::features::{ChannelFeatures, NodeFeatures};
        use lightning::ln::functional_test_utils::*;
        use lightning::ln::msgs::{ChannelMessageHandler, ErrorAction, LightningError};
        use lightning::routing::gossip::{EffectiveCapacity, NodeId};
-       use lightning::routing::router::{PaymentParameters, Route, RouteHop};
-       use lightning::routing::scoring::ChannelUsage;
+       use lightning::routing::router::{InFlightHtlcs, PaymentParameters, Route, RouteHop, Router};
+       use lightning::routing::scoring::{ChannelUsage, LockableScore, Score};
        use lightning::util::test_utils::TestLogger;
        use lightning::util::errors::APIError;
        use lightning::util::events::{Event, EventsProvider, MessageSendEvent, MessageSendEventsProvider};
        use secp256k1::{SecretKey, PublicKey, Secp256k1};
        use std::cell::RefCell;
        use std::collections::VecDeque;
+       use std::ops::DerefMut;
        use std::time::{SystemTime, Duration};
-       use time_utils::tests::SinceEpoch;
-       use DEFAULT_EXPIRY_TIME;
-       use lightning::util::errors::APIError::{ChannelUnavailable, MonitorUpdateFailed};
+       use crate::time_utils::tests::SinceEpoch;
+       use crate::DEFAULT_EXPIRY_TIME;
+       use lightning::util::errors::APIError::{ChannelUnavailable, MonitorUpdateInProgress};
 
        fn invoice(payment_preimage: PaymentPreimage) -> Invoice {
                let payment_hash = Sha256::hash(&payment_preimage.0);
@@ -866,7 +960,7 @@ mod tests {
        #[test]
        fn pays_invoice_on_first_attempt() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -874,16 +968,15 @@ mod tests {
                let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 
                let payer = TestPayer::new().expect_send(Amount::ForInvoice(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(0));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
 
-               invoice_payer.handle_event(&Event::PaymentSent {
+               invoice_payer.handle_event(Event::PaymentSent {
                        payment_id, payment_preimage, payment_hash, fee_paid_msat: None
                });
                assert_eq!(*event_handled.borrow(), true);
@@ -893,7 +986,7 @@ mod tests {
        #[test]
        fn pays_invoice_on_retry() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -903,11 +996,10 @@ mod tests {
                let payer = TestPayer::new()
                        .expect_send(Amount::ForInvoice(final_value_msat))
                        .expect_send(Amount::OnRetry(final_value_msat / 2));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
@@ -922,11 +1014,11 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(TestRouter::retry_for_invoice(&invoice)),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                assert_eq!(*event_handled.borrow(), false);
                assert_eq!(*payer.attempts.borrow(), 2);
 
-               invoice_payer.handle_event(&Event::PaymentSent {
+               invoice_payer.handle_event(Event::PaymentSent {
                        payment_id, payment_preimage, payment_hash, fee_paid_msat: None
                });
                assert_eq!(*event_handled.borrow(), true);
@@ -935,7 +1027,7 @@ mod tests {
 
        #[test]
        fn pays_invoice_on_partial_failure() {
-               let event_handler = |_: &_| { panic!() };
+               let event_handler = |_: Event| { panic!() };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -948,11 +1040,10 @@ mod tests {
                        .expect_send(Amount::ForInvoice(final_value_msat))
                        .expect_send(Amount::OnRetry(final_value_msat / 2))
                        .expect_send(Amount::OnRetry(final_value_msat / 2));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                assert!(invoice_payer.pay_invoice(&invoice).is_ok());
        }
@@ -960,7 +1051,7 @@ mod tests {
        #[test]
        fn retries_payment_path_for_unknown_payment() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -970,11 +1061,10 @@ mod tests {
                let payer = TestPayer::new()
                        .expect_send(Amount::OnRetry(final_value_msat / 2))
                        .expect_send(Amount::OnRetry(final_value_msat / 2));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(PaymentId([1; 32]));
                let event = Event::PaymentPathFailed {
@@ -987,15 +1077,15 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(TestRouter::retry_for_invoice(&invoice)),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event.clone());
                assert_eq!(*event_handled.borrow(), false);
                assert_eq!(*payer.attempts.borrow(), 1);
 
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event.clone());
                assert_eq!(*event_handled.borrow(), false);
                assert_eq!(*payer.attempts.borrow(), 2);
 
-               invoice_payer.handle_event(&Event::PaymentSent {
+               invoice_payer.handle_event(Event::PaymentSent {
                        payment_id, payment_preimage, payment_hash, fee_paid_msat: None
                });
                assert_eq!(*event_handled.borrow(), true);
@@ -1005,7 +1095,7 @@ mod tests {
        #[test]
        fn fails_paying_invoice_after_max_retry_counts() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1015,11 +1105,10 @@ mod tests {
                        .expect_send(Amount::ForInvoice(final_value_msat))
                        .expect_send(Amount::OnRetry(final_value_msat / 2))
                        .expect_send(Amount::OnRetry(final_value_msat / 2));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
@@ -1034,7 +1123,7 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(TestRouter::retry_for_invoice(&invoice)),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                assert_eq!(*event_handled.borrow(), false);
                assert_eq!(*payer.attempts.borrow(), 2);
 
@@ -1050,11 +1139,11 @@ mod tests {
                                final_value_msat: final_value_msat / 2, ..TestRouter::retry_for_invoice(&invoice)
                        }),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event.clone());
                assert_eq!(*event_handled.borrow(), false);
                assert_eq!(*payer.attempts.borrow(), 3);
 
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event.clone());
                assert_eq!(*event_handled.borrow(), true);
                assert_eq!(*payer.attempts.borrow(), 3);
        }
@@ -1063,7 +1152,7 @@ mod tests {
        #[test]
        fn fails_paying_invoice_after_max_retry_timeout() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1073,13 +1162,12 @@ mod tests {
                        .expect_send(Amount::ForInvoice(final_value_msat))
                        .expect_send(Amount::OnRetry(final_value_msat / 2));
 
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
-               type InvoicePayerUsingSinceEpoch <P, R, S, L, E> = InvoicePayerUsingTime::<P, R, S, L, E, SinceEpoch>;
+               type InvoicePayerUsingSinceEpoch <P, R, L, E> = InvoicePayerUsingTime::<P, R, L, E, SinceEpoch>;
 
                let invoice_payer =
-                       InvoicePayerUsingSinceEpoch::new(&payer, router, &scorer, &logger, event_handler, Retry::Timeout(Duration::from_secs(120)));
+                       InvoicePayerUsingSinceEpoch::new(&payer, router, &logger, event_handler, Retry::Timeout(Duration::from_secs(120)));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
@@ -1094,13 +1182,13 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(TestRouter::retry_for_invoice(&invoice)),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event.clone());
                assert_eq!(*event_handled.borrow(), false);
                assert_eq!(*payer.attempts.borrow(), 2);
 
                SinceEpoch::advance(Duration::from_secs(121));
 
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event.clone());
                assert_eq!(*event_handled.borrow(), true);
                assert_eq!(*payer.attempts.borrow(), 2);
        }
@@ -1108,18 +1196,17 @@ mod tests {
        #[test]
        fn fails_paying_invoice_with_missing_retry_params() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
                let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 
                let payer = TestPayer::new().expect_send(Amount::ForInvoice(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
@@ -1134,7 +1221,7 @@ mod tests {
                        short_channel_id: None,
                        retry: None,
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                assert_eq!(*event_handled.borrow(), true);
                assert_eq!(*payer.attempts.borrow(), 1);
        }
@@ -1144,14 +1231,13 @@ mod tests {
        #[test]
        fn fails_paying_invoice_after_expiration() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payer = TestPayer::new();
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = expired_invoice(payment_preimage);
@@ -1165,18 +1251,17 @@ mod tests {
        #[test]
        fn fails_retrying_invoice_after_expiration() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
                let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 
                let payer = TestPayer::new().expect_send(Amount::ForInvoice(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router,  &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
@@ -1195,7 +1280,7 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(retry_data),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                assert_eq!(*event_handled.borrow(), true);
                assert_eq!(*payer.attempts.borrow(), 1);
        }
@@ -1203,7 +1288,7 @@ mod tests {
        #[test]
        fn fails_paying_invoice_after_retry_error() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1213,11 +1298,10 @@ mod tests {
                        .fails_on_attempt(2)
                        .expect_send(Amount::ForInvoice(final_value_msat))
                        .expect_send(Amount::OnRetry(final_value_msat / 2));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
@@ -1232,7 +1316,7 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(TestRouter::retry_for_invoice(&invoice)),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                assert_eq!(*event_handled.borrow(), true);
                assert_eq!(*payer.attempts.borrow(), 2);
        }
@@ -1240,18 +1324,17 @@ mod tests {
        #[test]
        fn fails_paying_invoice_after_rejected_by_payee() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
                let final_value_msat = invoice.amount_milli_satoshis().unwrap();
 
                let payer = TestPayer::new().expect_send(Amount::ForInvoice(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
@@ -1266,7 +1349,7 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(TestRouter::retry_for_invoice(&invoice)),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                assert_eq!(*event_handled.borrow(), true);
                assert_eq!(*payer.attempts.borrow(), 1);
        }
@@ -1274,7 +1357,7 @@ mod tests {
        #[test]
        fn fails_repaying_invoice_with_pending_payment() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1283,11 +1366,10 @@ mod tests {
                let payer = TestPayer::new()
                        .expect_send(Amount::ForInvoice(final_value_msat))
                        .expect_send(Amount::ForInvoice(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(0));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
 
@@ -1315,7 +1397,7 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(TestRouter::retry_for_invoice(&invoice)),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                assert_eq!(*event_handled.borrow(), true);
        }
 
@@ -1323,10 +1405,9 @@ mod tests {
        fn fails_paying_invoice_with_routing_errors() {
                let payer = TestPayer::new();
                let router = FailingRouter {};
-               let scorer = RefCell::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, |_: &_| {}, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, |_: Event| {}, Retry::Attempts(0));
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1346,11 +1427,10 @@ mod tests {
                let payer = TestPayer::new()
                        .fails_on_attempt(1)
                        .expect_send(Amount::ForInvoice(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, |_: &_| {}, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, |_: Event| {}, Retry::Attempts(0));
 
                match invoice_payer.pay_invoice(&invoice) {
                        Err(PaymentError::Sending(_)) => {},
@@ -1362,7 +1442,7 @@ mod tests {
        #[test]
        fn pays_zero_value_invoice_using_amount() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = zero_value_invoice(payment_preimage);
@@ -1370,17 +1450,16 @@ mod tests {
                let final_value_msat = 100;
 
                let payer = TestPayer::new().expect_send(Amount::ForInvoice(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(0));
 
                let payment_id =
                        Some(invoice_payer.pay_zero_value_invoice(&invoice, final_value_msat).unwrap());
                assert_eq!(*payer.attempts.borrow(), 1);
 
-               invoice_payer.handle_event(&Event::PaymentSent {
+               invoice_payer.handle_event(Event::PaymentSent {
                        payment_id, payment_preimage, payment_hash, fee_paid_msat: None
                });
                assert_eq!(*event_handled.borrow(), true);
@@ -1390,14 +1469,13 @@ mod tests {
        #[test]
        fn fails_paying_zero_value_invoice_with_amount() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payer = TestPayer::new();
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router,  &logger, event_handler, Retry::Attempts(0));
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1413,7 +1491,7 @@ mod tests {
        #[test]
        fn pays_pubkey_with_amount() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let pubkey = pubkey();
                let payment_preimage = PaymentPreimage([1; 32]);
@@ -1424,11 +1502,10 @@ mod tests {
                let payer = TestPayer::new()
                        .expect_send(Amount::Spontaneous(final_value_msat))
                        .expect_send(Amount::OnRetry(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(invoice_payer.pay_pubkey(
                                pubkey, payment_preimage, final_value_msat, final_cltv_expiry_delta
@@ -1450,11 +1527,11 @@ mod tests {
                        short_channel_id: None,
                        retry: Some(retry),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                assert_eq!(*event_handled.borrow(), false);
                assert_eq!(*payer.attempts.borrow(), 2);
 
-               invoice_payer.handle_event(&Event::PaymentSent {
+               invoice_payer.handle_event(Event::PaymentSent {
                        payment_id, payment_preimage, payment_hash, fee_paid_msat: None
                });
                assert_eq!(*event_handled.borrow(), true);
@@ -1464,7 +1541,7 @@ mod tests {
        #[test]
        fn scores_failed_channel() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1477,13 +1554,13 @@ mod tests {
                let payer = TestPayer::new()
                        .expect_send(Amount::ForInvoice(final_value_msat))
                        .expect_send(Amount::OnRetry(final_value_msat / 2));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new().expect(TestResult::PaymentFailure {
+               let scorer = TestScorer::new().expect(TestResult::PaymentFailure {
                        path: path.clone(), short_channel_id: path[0].short_channel_id,
-               }));
+               });
+               let router = TestRouter::new(scorer);
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = Some(invoice_payer.pay_invoice(&invoice).unwrap());
                let event = Event::PaymentPathFailed {
@@ -1496,13 +1573,13 @@ mod tests {
                        short_channel_id,
                        retry: Some(TestRouter::retry_for_invoice(&invoice)),
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
        }
 
        #[test]
        fn scores_successful_channels() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1512,30 +1589,29 @@ mod tests {
 
                // Expect that scorer is given short_channel_id upon handling the event.
                let payer = TestPayer::new().expect_send(Amount::ForInvoice(final_value_msat));
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new()
+               let scorer = TestScorer::new()
                        .expect(TestResult::PaymentSuccess { path: route.paths[0].clone() })
-                       .expect(TestResult::PaymentSuccess { path: route.paths[1].clone() })
-               );
+                       .expect(TestResult::PaymentSuccess { path: route.paths[1].clone() });
+               let router = TestRouter::new(scorer);
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                let payment_id = invoice_payer.pay_invoice(&invoice).unwrap();
                let event = Event::PaymentPathSuccessful {
                        payment_id, payment_hash, path: route.paths[0].clone()
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
                let event = Event::PaymentPathSuccessful {
                        payment_id, payment_hash, path: route.paths[1].clone()
                };
-               invoice_payer.handle_event(&event);
+               invoice_payer.handle_event(event);
        }
 
        #[test]
        fn generates_correct_inflight_map_data() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice = invoice(payment_preimage);
@@ -1545,44 +1621,43 @@ mod tests {
                let payer = TestPayer::new().expect_send(Amount::ForInvoice(final_value_msat));
                let final_value_msat = invoice.amount_milli_satoshis().unwrap();
                let route = TestRouter::route_for_value(final_value_msat);
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(0));
 
                let payment_id = invoice_payer.pay_invoice(&invoice).unwrap();
 
                let inflight_map = invoice_payer.create_inflight_map();
                // First path check
-               assert_eq!(inflight_map.get(&(0, false)).unwrap().clone(), 94);
-               assert_eq!(inflight_map.get(&(1, true)).unwrap().clone(), 84);
-               assert_eq!(inflight_map.get(&(2, false)).unwrap().clone(), 64);
+               assert_eq!(inflight_map.0.get(&(0, false)).unwrap().clone(), 94);
+               assert_eq!(inflight_map.0.get(&(1, true)).unwrap().clone(), 84);
+               assert_eq!(inflight_map.0.get(&(2, false)).unwrap().clone(), 64);
 
                // Second path check
-               assert_eq!(inflight_map.get(&(3, false)).unwrap().clone(), 74);
-               assert_eq!(inflight_map.get(&(4, false)).unwrap().clone(), 64);
+               assert_eq!(inflight_map.0.get(&(3, false)).unwrap().clone(), 74);
+               assert_eq!(inflight_map.0.get(&(4, false)).unwrap().clone(), 64);
 
-               invoice_payer.handle_event(&Event::PaymentPathSuccessful {
+               invoice_payer.handle_event(Event::PaymentPathSuccessful {
                        payment_id, payment_hash, path: route.paths[0].clone()
                });
 
                let inflight_map = invoice_payer.create_inflight_map();
 
-               assert_eq!(inflight_map.get(&(0, false)), None);
-               assert_eq!(inflight_map.get(&(1, true)), None);
-               assert_eq!(inflight_map.get(&(2, false)), None);
+               assert_eq!(inflight_map.0.get(&(0, false)), None);
+               assert_eq!(inflight_map.0.get(&(1, true)), None);
+               assert_eq!(inflight_map.0.get(&(2, false)), None);
 
                // Second path should still be inflight
-               assert_eq!(inflight_map.get(&(3, false)).unwrap().clone(), 74);
-               assert_eq!(inflight_map.get(&(4, false)).unwrap().clone(), 64)
+               assert_eq!(inflight_map.0.get(&(3, false)).unwrap().clone(), 74);
+               assert_eq!(inflight_map.0.get(&(4, false)).unwrap().clone(), 64)
        }
 
        #[test]
        fn considers_inflight_htlcs_between_invoice_payments_when_path_succeeds() {
                // First, let's just send a payment through, but only make sure one of the path completes
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let payment_invoice = invoice(payment_preimage);
@@ -1594,8 +1669,7 @@ mod tests {
                        .expect_send(Amount::ForInvoice(final_value_msat));
                let final_value_msat = payment_invoice.amount_milli_satoshis().unwrap();
                let route = TestRouter::route_for_value(final_value_msat);
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new()
+               let scorer = TestScorer::new()
                        // 1st invoice, 1st path
                        .expect_usage(ChannelUsage { amount_msat: 64, inflight_htlc_msat: 0, effective_capacity: EffectiveCapacity::Unknown } )
                        .expect_usage(ChannelUsage { amount_msat: 84, inflight_htlc_msat: 0, effective_capacity: EffectiveCapacity::Unknown } )
@@ -1609,15 +1683,15 @@ mod tests {
                        .expect_usage(ChannelUsage { amount_msat: 94, inflight_htlc_msat: 0, effective_capacity: EffectiveCapacity::Unknown } )
                        // 2nd invoice, 2nd path
                        .expect_usage(ChannelUsage { amount_msat: 64, inflight_htlc_msat: 64, effective_capacity: EffectiveCapacity::Unknown } )
-                       .expect_usage(ChannelUsage { amount_msat: 74, inflight_htlc_msat: 74, effective_capacity: EffectiveCapacity::Unknown } )
-               );
+                       .expect_usage(ChannelUsage { amount_msat: 74, inflight_htlc_msat: 74, effective_capacity: EffectiveCapacity::Unknown } );
+               let router = TestRouter::new(scorer);
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(0));
 
                // Succeed 1st path, leave 2nd path inflight
                let payment_id = invoice_payer.pay_invoice(&payment_invoice).unwrap();
-               invoice_payer.handle_event(&Event::PaymentPathSuccessful {
+               invoice_payer.handle_event(Event::PaymentPathSuccessful {
                        payment_id, payment_hash, path: route.paths[0].clone()
                });
 
@@ -1634,7 +1708,7 @@ mod tests {
        fn considers_inflight_htlcs_between_retries() {
                // First, let's just send a payment through, but only make sure one of the path completes
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let payment_invoice = invoice(payment_preimage);
@@ -1646,8 +1720,7 @@ mod tests {
                        .expect_send(Amount::OnRetry(final_value_msat / 2))
                        .expect_send(Amount::OnRetry(final_value_msat / 4));
                let final_value_msat = payment_invoice.amount_milli_satoshis().unwrap();
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new()
+               let scorer = TestScorer::new()
                        // 1st invoice, 1st path
                        .expect_usage(ChannelUsage { amount_msat: 64, inflight_htlc_msat: 0, effective_capacity: EffectiveCapacity::Unknown } )
                        .expect_usage(ChannelUsage { amount_msat: 84, inflight_htlc_msat: 0, effective_capacity: EffectiveCapacity::Unknown } )
@@ -1668,15 +1741,15 @@ mod tests {
                        .expect_usage(ChannelUsage { amount_msat: 46, inflight_htlc_msat: 0, effective_capacity: EffectiveCapacity::Unknown } )
                        // Retry 2, 2nd path
                        .expect_usage(ChannelUsage { amount_msat: 16, inflight_htlc_msat: 64 + 32, effective_capacity: EffectiveCapacity::Unknown } )
-                       .expect_usage(ChannelUsage { amount_msat: 26, inflight_htlc_msat: 74 + 32 + 10, effective_capacity: EffectiveCapacity::Unknown } )
-               );
+                       .expect_usage(ChannelUsage { amount_msat: 26, inflight_htlc_msat: 74 + 32 + 10, effective_capacity: EffectiveCapacity::Unknown } );
+               let router = TestRouter::new(scorer);
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(2));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(2));
 
                // Fail 1st path, leave 2nd path inflight
                let payment_id = Some(invoice_payer.pay_invoice(&payment_invoice).unwrap());
-               invoice_payer.handle_event(&Event::PaymentPathFailed {
+               invoice_payer.handle_event(Event::PaymentPathFailed {
                        payment_id,
                        payment_hash,
                        network_update: None,
@@ -1688,7 +1761,7 @@ mod tests {
                });
 
                // Fails again the 1st path of our retry
-               invoice_payer.handle_event(&Event::PaymentPathFailed {
+               invoice_payer.handle_event(Event::PaymentPathFailed {
                        payment_id,
                        payment_hash,
                        network_update: None,
@@ -1706,7 +1779,7 @@ mod tests {
        #[test]
        fn accounts_for_some_inflight_htlcs_sent_during_partial_failure() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice_to_pay = invoice(payment_preimage);
@@ -1717,28 +1790,27 @@ mod tests {
                        .fails_with_partial_failure(
                                retry.clone(), OnAttempt(1),
                                Some(vec![
-                                       Err(ChannelUnavailable { err: "abc".to_string() }), Err(MonitorUpdateFailed)
+                                       Err(ChannelUnavailable { err: "abc".to_string() }), Err(MonitorUpdateInProgress)
                                ]))
                        .expect_send(Amount::ForInvoice(final_value_msat));
 
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(0));
 
                invoice_payer.pay_invoice(&invoice_to_pay).unwrap();
                let inflight_map = invoice_payer.create_inflight_map();
 
-               // Only the second path, which failed with `MonitorUpdateFailed` should be added to our
+               // Only the second path, which failed with `MonitorUpdateInProgress` should be added to our
                // inflight map because retries are disabled.
-               assert_eq!(inflight_map.len(), 2);
+               assert_eq!(inflight_map.0.len(), 2);
        }
 
        #[test]
        fn accounts_for_all_inflight_htlcs_sent_during_partial_failure() {
                let event_handled = core::cell::RefCell::new(false);
-               let event_handler = |_: &_| { *event_handled.borrow_mut() = true; };
+               let event_handler = |_: Event| { *event_handled.borrow_mut() = true; };
 
                let payment_preimage = PaymentPreimage([1; 32]);
                let invoice_to_pay = invoice(payment_preimage);
@@ -1749,26 +1821,31 @@ mod tests {
                        .fails_with_partial_failure(
                                retry.clone(), OnAttempt(1),
                                Some(vec![
-                                       Ok(()), Err(MonitorUpdateFailed)
+                                       Ok(()), Err(MonitorUpdateInProgress)
                                ]))
                        .expect_send(Amount::ForInvoice(final_value_msat));
 
-               let router = TestRouter {};
-               let scorer = RefCell::new(TestScorer::new());
+               let router = TestRouter::new(TestScorer::new());
                let logger = TestLogger::new();
                let invoice_payer =
-                       InvoicePayer::new(&payer, router, &scorer, &logger, event_handler, Retry::Attempts(0));
+                       InvoicePayer::new(&payer, router, &logger, event_handler, Retry::Attempts(0));
 
                invoice_payer.pay_invoice(&invoice_to_pay).unwrap();
                let inflight_map = invoice_payer.create_inflight_map();
 
                // All paths successful, hence we check of the existence of all 5 hops.
-               assert_eq!(inflight_map.len(), 5);
+               assert_eq!(inflight_map.0.len(), 5);
        }
 
-       struct TestRouter;
+       struct TestRouter {
+               scorer: RefCell<TestScorer>,
+       }
 
        impl TestRouter {
+               fn new(scorer: TestScorer) -> Self {
+                       TestRouter { scorer: RefCell::new(scorer) }
+               }
+
                fn route_for_value(final_value_msat: u64) -> Route {
                        Route {
                                paths: vec![
@@ -1842,12 +1919,14 @@ mod tests {
        }
 
        impl Router for TestRouter {
-               fn find_route<S: Score>(
-                       &self, payer: &PublicKey, route_params: &RouteParameters, _payment_hash: &PaymentHash,
-                       _first_hops: Option<&[&ChannelDetails]>, scorer: &S
+               fn find_route(
+                       &self, payer: &PublicKey, route_params: &RouteParameters,
+                       _first_hops: Option<&[&ChannelDetails]>, inflight_htlcs: InFlightHtlcs
                ) -> Result<Route, LightningError> {
                        // Simulate calling the Scorer just as you would in find_route
                        let route = Self::route_for_value(route_params.final_value_msat);
+                       let mut locked_scorer = self.scorer.lock();
+                       let scorer = ScorerAccountingForInFlightHtlcs::new(locked_scorer.deref_mut(), inflight_htlcs);
                        for path in route.paths {
                                let mut aggregate_msat = 0u64;
                                for (idx, hop) in path.iter().rev().enumerate() {
@@ -1874,17 +1953,45 @@ mod tests {
                }
        }
 
+       impl ScoringRouter for TestRouter {
+               fn notify_payment_path_failed(&self, path: &[&RouteHop], short_channel_id: u64) {
+                       self.scorer.lock().payment_path_failed(path, short_channel_id);
+               }
+
+               fn notify_payment_path_successful(&self, path: &[&RouteHop]) {
+                       self.scorer.lock().payment_path_successful(path);
+               }
+
+               fn notify_payment_probe_successful(&self, path: &[&RouteHop]) {
+                       self.scorer.lock().probe_successful(path);
+               }
+
+               fn notify_payment_probe_failed(&self, path: &[&RouteHop], short_channel_id: u64) {
+                       self.scorer.lock().probe_failed(path, short_channel_id);
+               }
+       }
+
        struct FailingRouter;
 
        impl Router for FailingRouter {
-               fn find_route<S: Score>(
-                       &self, _payer: &PublicKey, _params: &RouteParameters, _payment_hash: &PaymentHash,
-                       _first_hops: Option<&[&ChannelDetails]>, _scorer: &S
+               fn find_route(
+                       &self, _payer: &PublicKey, _params: &RouteParameters, _first_hops: Option<&[&ChannelDetails]>,
+                       _inflight_htlcs: InFlightHtlcs,
                ) -> Result<Route, LightningError> {
                        Err(LightningError { err: String::new(), action: ErrorAction::IgnoreError })
                }
        }
 
+       impl ScoringRouter for FailingRouter {
+               fn notify_payment_path_failed(&self, _path: &[&RouteHop], _short_channel_id: u64) {}
+
+               fn notify_payment_path_successful(&self, _path: &[&RouteHop]) {}
+
+               fn notify_payment_probe_successful(&self, _path: &[&RouteHop]) {}
+
+               fn notify_payment_probe_failed(&self, _path: &[&RouteHop], _short_channel_id: u64) {}
+       }
+
        struct TestScorer {
                event_expectations: Option<VecDeque<TestResult>>,
                scorer_expectations: RefCell<Option<VecDeque<ChannelUsage>>>,
@@ -1917,7 +2024,7 @@ mod tests {
 
        #[cfg(c_bindings)]
        impl lightning::util::ser::Writeable for TestScorer {
-               fn write<W: lightning::util::ser::Writer>(&self, _: &mut W) -> Result<(), std::io::Error> { unreachable!(); }
+               fn write<W: lightning::util::ser::Writer>(&self, _: &mut W) -> Result<(), lightning::io::Error> { unreachable!(); }
        }
 
        impl Score for TestScorer {
@@ -1946,7 +2053,7 @@ mod tests {
                                        Some(TestResult::PaymentSuccess { path }) => {
                                                panic!("Unexpected successful payment path: {:?}", path)
                                        },
-                                       None => panic!("Unexpected payment_path_failed call: {:?}", actual_path),
+                                       None => panic!("Unexpected notify_payment_path_failed call: {:?}", actual_path),
                                }
                        }
                }
@@ -1960,7 +2067,7 @@ mod tests {
                                        Some(TestResult::PaymentSuccess { path }) => {
                                                assert_eq!(actual_path, &path.iter().collect::<Vec<_>>()[..]);
                                        },
-                                       None => panic!("Unexpected payment_path_successful call: {:?}", actual_path),
+                                       None => panic!("Unexpected notify_payment_path_successful call: {:?}", actual_path),
                                }
                        }
                }
@@ -1974,7 +2081,7 @@ mod tests {
                                        Some(TestResult::PaymentSuccess { path }) => {
                                                panic!("Unexpected successful payment path: {:?}", path)
                                        },
-                                       None => panic!("Unexpected payment_path_failed call: {:?}", actual_path),
+                                       None => panic!("Unexpected notify_payment_path_failed call: {:?}", actual_path),
                                }
                        }
                }
@@ -1987,7 +2094,7 @@ mod tests {
                                        Some(TestResult::PaymentSuccess { path }) => {
                                                panic!("Unexpected successful payment path: {:?}", path)
                                        },
-                                       None => panic!("Unexpected payment_path_successful call: {:?}", actual_path),
+                                       None => panic!("Unexpected notify_payment_path_successful call: {:?}", actual_path),
                                }
                        }
                }
@@ -2043,7 +2150,7 @@ mod tests {
                }
 
                fn fails_on_attempt(self, attempt: usize) -> Self {
-                       let failure = PaymentSendFailure::ParameterError(APIError::MonitorUpdateFailed);
+                       let failure = PaymentSendFailure::ParameterError(APIError::MonitorUpdateInProgress);
                        self.fails_with(failure, OnAttempt(attempt))
                }
 
@@ -2060,13 +2167,13 @@ mod tests {
                        self
                }
 
-               fn check_attempts(&self) -> Result<PaymentId, PaymentSendFailure> {
+               fn check_attempts(&self) -> Result<(), PaymentSendFailure> {
                        let mut attempts = self.attempts.borrow_mut();
                        *attempts += 1;
 
                        match self.failing_on_attempt.borrow_mut().remove(&*attempts) {
                                Some(failure) => Err(failure),
-                               None => Ok(PaymentId([1; 32])),
+                               None => Ok(())
                        }
                }
 
@@ -2104,15 +2211,15 @@ mod tests {
 
                fn send_payment(
                        &self, route: &Route, _payment_hash: PaymentHash,
-                       _payment_secret: &Option<PaymentSecret>
-               ) -> Result<PaymentId, PaymentSendFailure> {
+                       _payment_secret: &Option<PaymentSecret>, _payment_id: PaymentId,
+               ) -> Result<(), PaymentSendFailure> {
                        self.check_value_msats(Amount::ForInvoice(route.get_total_amount()));
                        self.check_attempts()
                }
 
                fn send_spontaneous_payment(
-                       &self, route: &Route, _payment_preimage: PaymentPreimage,
-               ) -> Result<PaymentId, PaymentSendFailure> {
+                       &self, route: &Route, _payment_preimage: PaymentPreimage, _payment_id: PaymentId,
+               ) -> Result<(), PaymentSendFailure> {
                        self.check_value_msats(Amount::Spontaneous(route.get_total_amount()));
                        self.check_attempts()
                }
@@ -2121,7 +2228,7 @@ mod tests {
                        &self, route: &Route, _payment_id: PaymentId
                ) -> Result<(), PaymentSendFailure> {
                        self.check_value_msats(Amount::OnRetry(route.get_total_amount()));
-                       self.check_attempts().map(|_| ())
+                       self.check_attempts()
                }
 
                fn abandon_payment(&self, _payment_id: PaymentId) { }
@@ -2131,13 +2238,22 @@ mod tests {
        struct ManualRouter(RefCell<VecDeque<Result<Route, LightningError>>>);
 
        impl Router for ManualRouter {
-               fn find_route<S: Score>(
-                       &self, _payer: &PublicKey, _params: &RouteParameters, _payment_hash: &PaymentHash,
-                       _first_hops: Option<&[&ChannelDetails]>, _scorer: &S
+               fn find_route(
+                       &self, _payer: &PublicKey, _params: &RouteParameters, _first_hops: Option<&[&ChannelDetails]>,
+                       _inflight_htlcs: InFlightHtlcs
                ) -> Result<Route, LightningError> {
                        self.0.borrow_mut().pop_front().unwrap()
                }
        }
+       impl ScoringRouter for ManualRouter {
+               fn notify_payment_path_failed(&self, _path: &[&RouteHop], _short_channel_id: u64) {}
+
+               fn notify_payment_path_successful(&self, _path: &[&RouteHop]) {}
+
+               fn notify_payment_probe_successful(&self, _path: &[&RouteHop]) {}
+
+               fn notify_payment_probe_failed(&self, _path: &[&RouteHop], _short_channel_id: u64) {}
+       }
        impl ManualRouter {
                fn expect_find_route(&self, result: Result<Route, LightningError>) {
                        self.0.borrow_mut().push_back(result);
@@ -2160,24 +2276,24 @@ mod tests {
                let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None, None]);
                let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
 
-               create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0, InitFeatures::known(), InitFeatures::known());
-               create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0, InitFeatures::known(), InitFeatures::known());
+               create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0, channelmanager::provided_init_features(), channelmanager::provided_init_features());
+               create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0, channelmanager::provided_init_features(), channelmanager::provided_init_features());
                let chans = nodes[0].node.list_usable_channels();
                let mut route = Route {
                        paths: vec![
                                vec![RouteHop {
                                        pubkey: nodes[1].node.get_our_node_id(),
-                                       node_features: NodeFeatures::known(),
+                                       node_features: channelmanager::provided_node_features(),
                                        short_channel_id: chans[0].short_channel_id.unwrap(),
-                                       channel_features: ChannelFeatures::known(),
+                                       channel_features: channelmanager::provided_channel_features(),
                                        fee_msat: 10_000,
                                        cltv_expiry_delta: 100,
                                }],
                                vec![RouteHop {
                                        pubkey: nodes[1].node.get_our_node_id(),
-                                       node_features: NodeFeatures::known(),
+                                       node_features: channelmanager::provided_node_features(),
                                        short_channel_id: chans[1].short_channel_id.unwrap(),
-                                       channel_features: ChannelFeatures::known(),
+                                       channel_features: channelmanager::provided_channel_features(),
                                        fee_msat: 100_000_001, // Our default max-HTLC-value is 10% of the channel value, which this is one more than
                                        cltv_expiry_delta: 100,
                                }],
@@ -2191,13 +2307,12 @@ mod tests {
                route.paths[1][0].fee_msat = 50_000_000;
                router.expect_find_route(Ok(route.clone()));
 
-               let event_handler = |_: &_| { panic!(); };
-               let scorer = RefCell::new(TestScorer::new());
-               let invoice_payer = InvoicePayer::new(nodes[0].node, router, &scorer, nodes[0].logger, event_handler, Retry::Attempts(1));
+               let event_handler = |_: Event| { panic!(); };
+               let invoice_payer = InvoicePayer::new(nodes[0].node, router, nodes[0].logger, event_handler, Retry::Attempts(1));
 
                assert!(invoice_payer.pay_invoice(&create_invoice_from_channelmanager_and_duration_since_epoch(
-                       &nodes[1].node, nodes[1].keys_manager, Currency::Bitcoin, Some(100_010_000), "Invoice".to_string(),
-                       duration_since_epoch(), 3600).unwrap())
+                       &nodes[1].node, nodes[1].keys_manager, nodes[1].logger, Currency::Bitcoin,
+                       Some(100_010_000), "Invoice".to_string(), duration_since_epoch(), 3600).unwrap())
                        .is_ok());
                let htlc_msgs = nodes[0].node.get_and_clear_pending_msg_events();
                assert_eq!(htlc_msgs.len(), 2);
@@ -2212,16 +2327,16 @@ mod tests {
                let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None, None]);
                let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
 
-               create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0, InitFeatures::known(), InitFeatures::known());
-               create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0, InitFeatures::known(), InitFeatures::known());
+               create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0, channelmanager::provided_init_features(), channelmanager::provided_init_features());
+               create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0, channelmanager::provided_init_features(), channelmanager::provided_init_features());
                let chans = nodes[0].node.list_usable_channels();
                let mut route = Route {
                        paths: vec![
                                vec![RouteHop {
                                        pubkey: nodes[1].node.get_our_node_id(),
-                                       node_features: NodeFeatures::known(),
+                                       node_features: channelmanager::provided_node_features(),
                                        short_channel_id: chans[0].short_channel_id.unwrap(),
-                                       channel_features: ChannelFeatures::known(),
+                                       channel_features: channelmanager::provided_channel_features(),
                                        fee_msat: 100_000_001, // Our default max-HTLC-value is 10% of the channel value, which this is one more than
                                        cltv_expiry_delta: 100,
                                }],
@@ -2237,13 +2352,12 @@ mod tests {
                route.paths[1][0].fee_msat = 50_000_001;
                router.expect_find_route(Ok(route.clone()));
 
-               let event_handler = |_: &_| { panic!(); };
-               let scorer = RefCell::new(TestScorer::new());
-               let invoice_payer = InvoicePayer::new(nodes[0].node, router, &scorer, nodes[0].logger, event_handler, Retry::Attempts(1));
+               let event_handler = |_: Event| { panic!(); };
+               let invoice_payer = InvoicePayer::new(nodes[0].node, router, nodes[0].logger, event_handler, Retry::Attempts(1));
 
                assert!(invoice_payer.pay_invoice(&create_invoice_from_channelmanager_and_duration_since_epoch(
-                       &nodes[1].node, nodes[1].keys_manager, Currency::Bitcoin, Some(100_010_000), "Invoice".to_string(),
-                       duration_since_epoch(), 3600).unwrap())
+                       &nodes[1].node, nodes[1].keys_manager, nodes[1].logger, Currency::Bitcoin,
+                       Some(100_010_000), "Invoice".to_string(), duration_since_epoch(), 3600).unwrap())
                        .is_ok());
                let htlc_msgs = nodes[0].node.get_and_clear_pending_msg_events();
                assert_eq!(htlc_msgs.len(), 2);
@@ -2271,38 +2385,38 @@ mod tests {
                let node_chanmgrs = create_node_chanmgrs(3, &node_cfgs, &[None, None, None]);
                let nodes = create_network(3, &node_cfgs, &node_chanmgrs);
 
-               let chan_1_scid = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 10_000_000, 0, InitFeatures::known(), InitFeatures::known()).0.contents.short_channel_id;
-               let chan_2_scid = create_announced_chan_between_nodes_with_value(&nodes, 1, 2, 10_000_000, 0, InitFeatures::known(), InitFeatures::known()).0.contents.short_channel_id;
+               let chan_1_scid = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 10_000_000, 0, channelmanager::provided_init_features(), channelmanager::provided_init_features()).0.contents.short_channel_id;
+               let chan_2_scid = create_announced_chan_between_nodes_with_value(&nodes, 1, 2, 10_000_000, 0, channelmanager::provided_init_features(), channelmanager::provided_init_features()).0.contents.short_channel_id;
 
                let mut route = Route {
                        paths: vec![
                                vec![RouteHop {
                                        pubkey: nodes[1].node.get_our_node_id(),
-                                       node_features: NodeFeatures::known(),
+                                       node_features: channelmanager::provided_node_features(),
                                        short_channel_id: chan_1_scid,
-                                       channel_features: ChannelFeatures::known(),
+                                       channel_features: channelmanager::provided_channel_features(),
                                        fee_msat: 0,
                                        cltv_expiry_delta: 100,
                                }, RouteHop {
                                        pubkey: nodes[2].node.get_our_node_id(),
-                                       node_features: NodeFeatures::known(),
+                                       node_features: channelmanager::provided_node_features(),
                                        short_channel_id: chan_2_scid,
-                                       channel_features: ChannelFeatures::known(),
+                                       channel_features: channelmanager::provided_channel_features(),
                                        fee_msat: 100_000_000,
                                        cltv_expiry_delta: 100,
                                }],
                                vec![RouteHop {
                                        pubkey: nodes[1].node.get_our_node_id(),
-                                       node_features: NodeFeatures::known(),
+                                       node_features: channelmanager::provided_node_features(),
                                        short_channel_id: chan_1_scid,
-                                       channel_features: ChannelFeatures::known(),
+                                       channel_features: channelmanager::provided_channel_features(),
                                        fee_msat: 0,
                                        cltv_expiry_delta: 100,
                                }, RouteHop {
                                        pubkey: nodes[2].node.get_our_node_id(),
-                                       node_features: NodeFeatures::known(),
+                                       node_features: channelmanager::provided_node_features(),
                                        short_channel_id: chan_2_scid,
-                                       channel_features: ChannelFeatures::known(),
+                                       channel_features: channelmanager::provided_channel_features(),
                                        fee_msat: 100_000_000,
                                        cltv_expiry_delta: 100,
                                }]
@@ -2315,17 +2429,16 @@ mod tests {
                route.paths.remove(1);
                router.expect_find_route(Ok(route.clone()));
 
-               let expected_events: RefCell<VecDeque<&dyn Fn(&Event)>> = RefCell::new(VecDeque::new());
-               let event_handler = |event: &Event| {
+               let expected_events: RefCell<VecDeque<&dyn Fn(Event)>> = RefCell::new(VecDeque::new());
+               let event_handler = |event: Event| {
                        let event_checker = expected_events.borrow_mut().pop_front().unwrap();
                        event_checker(event);
                };
-               let scorer = RefCell::new(TestScorer::new());
-               let invoice_payer = InvoicePayer::new(nodes[0].node, router, &scorer, nodes[0].logger, event_handler, Retry::Attempts(1));
+               let invoice_payer = InvoicePayer::new(nodes[0].node, router, nodes[0].logger, event_handler, Retry::Attempts(1));
 
                assert!(invoice_payer.pay_invoice(&create_invoice_from_channelmanager_and_duration_since_epoch(
-                       &nodes[1].node, nodes[1].keys_manager, Currency::Bitcoin, Some(100_010_000), "Invoice".to_string(),
-                       duration_since_epoch(), 3600).unwrap())
+                       &nodes[1].node, nodes[1].keys_manager, nodes[1].logger, Currency::Bitcoin,
+                       Some(100_010_000), "Invoice".to_string(), duration_since_epoch(), 3600).unwrap())
                        .is_ok());
                let htlc_updates = SendEvent::from_node(&nodes[0]);
                check_added_monitors!(nodes[0], 1);
@@ -2392,7 +2505,7 @@ mod tests {
                // `PaymentPathFailed` being passed up to the user (us, in this case). Previously, we'd
                // treated this as "HTLC complete" and dropped the retry counter, causing us to retry again
                // if the final HTLC failed.
-               expected_events.borrow_mut().push_back(&|ev: &Event| {
+               expected_events.borrow_mut().push_back(&|ev: Event| {
                        if let Event::PaymentPathFailed { payment_failed_permanently, all_paths_failed, .. } = ev {
                                assert!(!payment_failed_permanently);
                                assert!(all_paths_failed);
@@ -2410,13 +2523,13 @@ mod tests {
                nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &bs_fail_update.update_fail_htlcs[0]);
                commitment_signed_dance!(nodes[0], nodes[1], &bs_fail_update.commitment_signed, false, true);
 
-               expected_events.borrow_mut().push_back(&|ev: &Event| {
+               expected_events.borrow_mut().push_back(&|ev: Event| {
                        if let Event::PaymentPathFailed { payment_failed_permanently, all_paths_failed, .. } = ev {
                                assert!(!payment_failed_permanently);
                                assert!(all_paths_failed);
                        } else { panic!("Unexpected event"); }
                });
-               expected_events.borrow_mut().push_back(&|ev: &Event| {
+               expected_events.borrow_mut().push_back(&|ev: Event| {
                        if let Event::PaymentFailed { .. } = ev {
                        } else { panic!("Unexpected event"); }
                });