im-online: use EstimateNextSessionRotation to get better estimates of session progress (#8242)

* frame-support: add method to estimate current session progress

* im-online: use EstimateNextSessionRotation trait to delay heartbeats

* node: fix im-online pallet instantiation

* frame-support: fix docs

* frame: fix tests

* pallet-session: last block of periodic session means 100% session progress

* pallet-session: add test for periodic session progress

* pallet-babe: fix epoch progress and add test

* frame-support: return weight with session estimates

* pallet-im-online: add test for session progress logic

substrate/frame/babe/src/lib.rs

@@ -34,7 +34,7 @@ use sp_application_crypto::Public;
 use sp_runtime::{
 	generic::DigestItem,
 	traits::{IsMember, One, SaturatedConversion, Saturating, Zero},
-	ConsensusEngineId, KeyTypeId,
+	ConsensusEngineId, KeyTypeId, Percent,
 };
 use sp_session::{GetSessionNumber, GetValidatorCount};
 use sp_std::prelude::*;
@@ -780,14 +780,25 @@ impl<T: Config> frame_support::traits::EstimateNextSessionRotation<T::BlockNumbe
 		T::EpochDuration::get().saturated_into()
 	}
 
-	fn estimate_next_session_rotation(now: T::BlockNumber) -> Option<T::BlockNumber> {
-		Self::next_expected_epoch_change(now)
+	fn estimate_current_session_progress(_now: T::BlockNumber) -> (Option<Percent>, Weight) {
+		let elapsed = CurrentSlot::get().saturating_sub(Self::current_epoch_start()) + 1;
+
+		(
+			Some(Percent::from_rational_approximation(
+				*elapsed,
+				T::EpochDuration::get(),
+			)),
+			// Read: Current Slot, Epoch Index, Genesis Slot
+			T::DbWeight::get().reads(3),
+		)
 	}
 
-	// The validity of this weight depends on the implementation of `estimate_next_session_rotation`
-	fn weight(_now: T::BlockNumber) -> Weight {
-		// Read: Current Slot, Epoch Index, Genesis Slot
-		T::DbWeight::get().reads(3)
+	fn estimate_next_session_rotation(now: T::BlockNumber) -> (Option<T::BlockNumber>, Weight) {
+		(
+			Self::next_expected_epoch_change(now),
+			// Read: Current Slot, Epoch Index, Genesis Slot
+			T::DbWeight::get().reads(3),
+		)
 	}
 }
 

substrate/frame/babe/src/mock.rs

@@ -260,7 +260,7 @@ impl Config for Test {
 pub fn go_to_block(n: u64, s: u64) {
 	use frame_support::traits::OnFinalize;
 
-	System::on_finalize(System::block_number());
+	Babe::on_finalize(System::block_number());
 	Session::on_finalize(System::block_number());
 	Staking::on_finalize(System::block_number());
 
@@ -274,14 +274,8 @@ pub fn go_to_block(n: u64, s: u64) {
 	let pre_digest = make_secondary_plain_pre_digest(0, s.into());
 
 	System::initialize(&n, &parent_hash, &pre_digest, InitKind::Full);
-	System::set_block_number(n);
-	Timestamp::set_timestamp(n);
 
-	if s > 1 {
-		CurrentSlot::put(Slot::from(s));
-	}
-
-	System::on_initialize(n);
+	Babe::on_initialize(n);
 	Session::on_initialize(n);
 	Staking::on_initialize(n);
 }

substrate/frame/babe/src/tests.rs

@@ -20,12 +20,12 @@
 use super::{Call, *};
 use frame_support::{
 	assert_err, assert_ok,
-	traits::{Currency, OnFinalize},
+	traits::{Currency, EstimateNextSessionRotation, OnFinalize},
 	weights::{GetDispatchInfo, Pays},
 };
 use mock::*;
 use pallet_session::ShouldEndSession;
-use sp_consensus_babe::{AllowedSlots, Slot, BabeEpochConfiguration};
+use sp_consensus_babe::{AllowedSlots, BabeEpochConfiguration, Slot};
 use sp_core::crypto::Pair;
 
 const EMPTY_RANDOMNESS: [u8; 32] = [
@@ -220,6 +220,38 @@ fn can_predict_next_epoch_change() {
 	})
 }
 
+#[test]
+fn can_estimate_current_epoch_progress() {
+	new_test_ext(1).execute_with(|| {
+		assert_eq!(<Test as Config>::EpochDuration::get(), 3);
+
+		// with BABE the genesis block is not part of any epoch, the first epoch starts at block #1,
+		// therefore its last block should be #3
+		for i in 1u64..4 {
+			progress_to_block(i);
+
+			assert_eq!(Babe::estimate_next_session_rotation(i).0.unwrap(), 4);
+
+			// the last block of the epoch must have 100% progress.
+			if Babe::estimate_next_session_rotation(i).0.unwrap() - 1 == i {
+				assert_eq!(
+					Babe::estimate_current_session_progress(i).0.unwrap(),
+					Percent::from_percent(100)
+				);
+			} else {
+				assert!(Babe::estimate_current_session_progress(i).0.unwrap() < Percent::from_percent(100));
+			}
+		}
+
+		// the first block of the new epoch counts towards the epoch progress as well
+		progress_to_block(4);
+		assert_eq!(
+			Babe::estimate_current_session_progress(4).0.unwrap(),
+			Percent::from_percent(33),
+		);
+	})
+}
+
 #[test]
 fn can_enact_next_config() {
 	new_test_ext(1).execute_with(|| {