Simplify Instant mocking in outbound payments

To handle `std` and `no-std` concepts of time in scoring, we'd
originally written a generic `Time` trait which we could use to
fetch the current time, observe real (not wall-clock) elapsed time,
and serialize the time.

Eventually, scoring stopped using this `Time` trait but outbound
payment retry expiry started using it instead to mock time in
tests.

Since scoring no longer uses the full features which required the
`Time` trait, we can substantially simplify by just having the
mocking option.

lightning/src/ln/outbound_payment.rs

@@ -26,9 +26,8 @@ use crate::routing::router::{BlindedTail, InFlightHtlcs, Path, PaymentParameters
 use crate::sign::{EntropySource, NodeSigner, Recipient};
 use crate::util::errors::APIError;
 use crate::util::logger::Logger;
-use crate::util::time::Time;
-#[cfg(all(feature = "std", test))]
-use crate::util::time::tests::SinceEpoch;
+#[cfg(feature = "std")]
+use crate::util::time::Instant;
 use crate::util::ser::ReadableArgs;
 
 use core::fmt::{self, Display, Formatter};
@@ -319,12 +318,9 @@ impl Retry {
 			(Retry::Attempts(max_retry_count), PaymentAttempts { count, .. }) => {
 				max_retry_count > count
 			},
-			#[cfg(all(feature = "std", not(test)))]
+			#[cfg(feature = "std")]
 			(Retry::Timeout(max_duration), PaymentAttempts { first_attempted_at, .. }) =>
-				*max_duration >= crate::util::time::MonotonicTime::now().duration_since(*first_attempted_at),
-			#[cfg(all(feature = "std", test))]
-			(Retry::Timeout(max_duration), PaymentAttempts { first_attempted_at, .. }) =>
-				*max_duration >= SinceEpoch::now().duration_since(*first_attempted_at),
+				*max_duration >= Instant::now().duration_since(*first_attempted_at),
 		}
 	}
 }
@@ -339,42 +335,28 @@ pub(super) fn has_expired(route_params: &RouteParameters) -> bool {
 	false
 }
 
-pub(crate) type PaymentAttempts = PaymentAttemptsUsingTime<ConfiguredTime>;
-
 /// Storing minimal payment attempts information required for determining if a outbound payment can
 /// be retried.
-pub(crate) struct PaymentAttemptsUsingTime<T: Time> {
+pub(crate) struct PaymentAttempts {
 	/// This count will be incremented only after the result of the attempt is known. When it's 0,
 	/// it means the result of the first attempt is not known yet.
 	pub(crate) count: u32,
 	/// This field is only used when retry is `Retry::Timeout` which is only build with feature std
 	#[cfg(feature = "std")]
-	first_attempted_at: T,
-	#[cfg(not(feature = "std"))]
-	phantom: core::marker::PhantomData<T>,
-
+	first_attempted_at: Instant,
 }
 
-#[cfg(not(feature = "std"))]
-type ConfiguredTime = crate::util::time::Eternity;
-#[cfg(all(feature = "std", not(test)))]
-type ConfiguredTime = crate::util::time::MonotonicTime;
-#[cfg(all(feature = "std", test))]
-type ConfiguredTime = SinceEpoch;
-
-impl<T: Time> PaymentAttemptsUsingTime<T> {
+impl PaymentAttempts {
 	pub(crate) fn new() -> Self {
-		PaymentAttemptsUsingTime {
+		PaymentAttempts {
 			count: 0,
 			#[cfg(feature = "std")]
-			first_attempted_at: T::now(),
-			#[cfg(not(feature = "std"))]
-			phantom: core::marker::PhantomData,
+			first_attempted_at: Instant::now(),
 		}
 	}
 }
 
-impl<T: Time> Display for PaymentAttemptsUsingTime<T> {
+impl Display for PaymentAttempts {
 	fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
 		#[cfg(not(feature = "std"))]
 		return write!(f, "attempts: {}", self.count);
@@ -383,7 +365,7 @@ impl<T: Time> Display for PaymentAttemptsUsingTime<T> {
 			f,
 			"attempts: {}, duration: {}s",
 			self.count,
-			T::now().duration_since(self.first_attempted_at).as_secs()
+			Instant::now().duration_since(self.first_attempted_at).as_secs()
 		);
 	}
 }

lightning/src/ln/payment_tests.rs

@@ -46,7 +46,7 @@ use crate::routing::gossip::NodeId;
 
 #[cfg(feature = "std")]
 use {
-	crate::util::time::tests::SinceEpoch,
+	crate::util::time::Instant as TestTime,
 	std::time::{SystemTime, Instant, Duration},
 };
 
@@ -2340,7 +2340,7 @@ fn do_automatic_retries(test: AutoRetry) {
 			pass_failed_attempt_with_retry_along_path!(channel_id_2, true);
 
 			// Advance the time so the second attempt fails due to timeout.
-			SinceEpoch::advance(Duration::from_secs(61));
+			TestTime::advance(Duration::from_secs(61));
 
 			// Make sure we don't retry again.
 			nodes[0].node.process_pending_htlc_forwards();

lightning/src/util/mod.rs

@@ -31,9 +31,11 @@ pub(crate) mod atomic_counter;
 pub(crate) mod async_poll;
 pub(crate) mod byte_utils;
 pub(crate) mod transaction_utils;
-pub(crate) mod time;
 pub mod hash_tables;
 
+#[cfg(feature = "std")]
+pub(crate) mod time;
+
 pub mod indexed_map;
 
 /// Logging macro utilities.

lightning/src/util/time.rs

@@ -4,93 +4,25 @@
 // You may not use this file except in accordance with one or both of these
 // licenses.
 
-//! [`Time`] trait and different implementations. Currently, it's mainly used in tests so we can
-//! manually advance time.
-//! Other crates may symlink this file to use it while [`Time`] trait is sealed here.
-
-use core::ops::Sub;
-use core::time::Duration;
-
-/// A measurement of time.
-pub trait Time: Copy + Sub<Duration, Output = Self> where Self: Sized {
-	/// Returns an instance corresponding to the current moment.
-	fn now() -> Self;
-
-	/// Returns the amount of time passed between `earlier` and `self`.
-	fn duration_since(&self, earlier: Self) -> Duration;
-}
-
-/// A state in which time has no meaning.
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub struct Eternity;
-
-impl Time for Eternity {
-	fn now() -> Self {
-		Self
-	}
-
-	fn duration_since(&self, _earlier: Self) -> Duration {
-		Duration::from_secs(0)
-	}
-}
-
-impl Sub<Duration> for Eternity {
-	type Output = Self;
-
-	fn sub(self, _other: Duration) -> Self {
-		self
-	}
-}
-
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-#[cfg(feature = "std")]
-pub struct MonotonicTime(std::time::Instant);
-
-/// The amount of time to shift `Instant` forward to prevent overflow when subtracting a `Duration`
-/// from `Instant::now` on some operating systems (e.g., iOS representing `Instance` as `u64`).
-#[cfg(feature = "std")]
-const SHIFT: Duration = Duration::from_secs(10 * 365 * 24 * 60 * 60); // 10 years.
-
-#[cfg(feature = "std")]
-impl Time for MonotonicTime {
-	fn now() -> Self {
-		let instant = std::time::Instant::now().checked_add(SHIFT).expect("Overflow on MonotonicTime instantiation");
-		Self(instant)
-	}
-
-	fn duration_since(&self, earlier: Self) -> Duration {
-		// On rust prior to 1.60 `Instant::duration_since` will panic if time goes backwards.
-		// However, we support rust versions prior to 1.60 and some users appear to have "monotonic
-		// clocks" that go backwards in practice (likely relatively ancient kernels/etc). Thus, we
-		// manually check for time going backwards here and return a duration of zero in that case.
-		let now = Self::now();
-		if now.0 > earlier.0 { now.0 - earlier.0 } else { Duration::from_secs(0) }
-	}
-}
-
-#[cfg(feature = "std")]
-impl Sub<Duration> for MonotonicTime {
-	type Output = Self;
-
-	fn sub(self, other: Duration) -> Self {
-		let instant = self.0.checked_sub(other).expect("MonotonicTime is not supposed to go backward futher than 10 years");
-		Self(instant)
-	}
-}
+//! A simple module which either re-exports [`std::time::Instant`] or a mocked version of it for
+//! tests.
 
 #[cfg(test)]
-pub mod tests {
-	use super::{Time, Eternity};
+pub use test::Instant;
+#[cfg(not(test))]
+pub use std::time::Instant;
 
+#[cfg(test)]
+mod test {
 	use core::time::Duration;
 	use core::ops::Sub;
 	use core::cell::Cell;
 
 	/// Time that can be advanced manually in tests.
 	#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-	pub struct SinceEpoch(Duration);
+	pub struct Instant(Duration);
 
-	impl SinceEpoch {
+	impl Instant {
 		thread_local! {
 			static ELAPSED: Cell<Duration> = core::cell::Cell::new(Duration::from_secs(0));
 		}
@@ -98,19 +30,17 @@ pub mod tests {
 		pub fn advance(duration: Duration) {
 			Self::ELAPSED.with(|elapsed| elapsed.set(elapsed.get() + duration))
 		}
-	}
 
-	impl Time for SinceEpoch {
-		fn now() -> Self {
+		pub fn now() -> Self {
 			Self(Self::ELAPSED.with(|elapsed| elapsed.get()))
 		}
 
-		fn duration_since(&self, earlier: Self) -> Duration {
+		pub fn duration_since(&self, earlier: Self) -> Duration {
 			self.0 - earlier.0
 		}
 	}
 
-	impl Sub<Duration> for SinceEpoch {
+	impl Sub<Duration> for Instant {
 		type Output = Self;
 
 		fn sub(self, other: Duration) -> Self {
@@ -120,21 +50,13 @@ pub mod tests {
 
 	#[test]
 	fn time_passes_when_advanced() {
-		let now = SinceEpoch::now();
+		let now = Instant::now();
 
-		SinceEpoch::advance(Duration::from_secs(1));
-		SinceEpoch::advance(Duration::from_secs(1));
+		Instant::advance(Duration::from_secs(1));
+		Instant::advance(Duration::from_secs(1));
 
-		let later = SinceEpoch::now();
+		let later = Instant::now();
 
 		assert_eq!(now.0 + Duration::from_secs(2), later.0);
 	}
-
-	#[test]
-	fn time_never_passes_in_an_eternity() {
-		let now = Eternity::now();
-		let later = Eternity::now();
-
-		assert_eq!(later, now);
-	}
 }