babe: expose next epoch data

bin/node/runtime/src/lib.rs

@@ -1160,6 +1160,10 @@ impl_runtime_apis! {
 			Babe::current_epoch()
 		}
 
+		fn next_epoch() -> sp_consensus_babe::Epoch {
+			Babe::next_epoch()
+		}
+
 		fn generate_key_ownership_proof(
 			_slot_number: sp_consensus_babe::SlotNumber,
 			authority_id: sp_consensus_babe::AuthorityId,

frame/babe/src/lib.rs

@@ -192,6 +192,9 @@ decl_storage! {
 		/// Next epoch randomness.
 		NextRandomness: schnorrkel::Randomness;
 
+		/// Next epoch authorities.
+		NextAuthorities: Vec<(AuthorityId, BabeAuthorityWeight)>;
+
 		/// Randomness under construction.
 		///
 		/// We make a tradeoff between storage accesses and list length.
@@ -464,9 +467,13 @@ impl<T: Config> Module<T> {
 		let randomness = Self::randomness_change_epoch(next_epoch_index);
 		Randomness::put(randomness);
 
+		// Update the next epoch authorities.
+		NextAuthorities::put(next_authorities);
+
 		// After we update the current epoch, we signal the *next* epoch change
 		// so that nodes can track changes.
 		let next_randomness = NextRandomness::get();
+		let next_authorities = NextAuthorities::get();
 
 		let next_epoch = NextEpochDescriptor {
 			authorities: next_authorities,
@@ -483,7 +490,7 @@ impl<T: Config> Module<T> {
 	// give correct results after `do_initialize` of the first block
 	// in the chain (as its result is based off of `GenesisSlot`).
 	pub fn current_epoch_start() -> SlotNumber {
-		(EpochIndex::get() * T::EpochDuration::get()) + GenesisSlot::get()
+		Self::epoch_start(EpochIndex::get())
 	}
 
 	/// Produces information about the current epoch.
@@ -497,6 +504,24 @@ impl<T: Config> Module<T> {
 		}
 	}
 
+	/// Produces information about the next epoch (which was already previously
+	/// announced).
+	pub fn next_epoch() -> Epoch {
+		let next_epoch_index = EpochIndex::get() + 1;
+
+		Epoch {
+			epoch_index: next_epoch_index,
+			start_slot: Self::epoch_start(next_epoch_index),
+			duration: T::EpochDuration::get(),
+			authorities: NextAuthorities::get(),
+			randomness: NextRandomness::get(),
+		}
+	}
+
+	fn epoch_start(epoch_index: u64) -> SlotNumber {
+		(epoch_index * T::EpochDuration::get()) + GenesisSlot::get()
+	}
+
 	fn deposit_consensus<U: Encode>(new: U) {
 		let log: DigestItem<T::Hash> = DigestItem::Consensus(BABE_ENGINE_ID, new.encode());
 		<frame_system::Module<T>>::deposit_log(log.into())

primitives/consensus/babe/src/lib.rs

@@ -382,6 +382,10 @@ sp_api::decl_runtime_apis! {
 		/// Returns information regarding the current epoch.
 		fn current_epoch() -> Epoch;
 
+		/// Returns information regarding the next epoch (which was already
+		/// previously announced).
+		fn next_epoch() -> Epoch;
+
 		/// Generates a proof of key ownership for the given authority in the
 		/// current epoch. An example usage of this module is coupled with the
 		/// session historical module to prove that a given authority key is

test-utils/runtime/src/lib.rs

@@ -741,6 +741,10 @@ cfg_if! {
 					<pallet_babe::Module<Runtime>>::current_epoch()
 				}
 
+				fn next_epoch() -> sp_consensus_babe::Epoch {
+					<pallet_babe::Module<Runtime>>::next_epoch()
+				}
+
 				fn submit_report_equivocation_unsigned_extrinsic(
 					_equivocation_proof: sp_consensus_babe::EquivocationProof<
 						<Block as BlockT>::Header,
@@ -996,6 +1000,10 @@ cfg_if! {
 					<pallet_babe::Module<Runtime>>::current_epoch()
 				}
 
+				fn next_epoch() -> sp_consensus_babe::Epoch {
+					<pallet_babe::Module<Runtime>>::next_epoch()
+				}
+
 				fn submit_report_equivocation_unsigned_extrinsic(
 					_equivocation_proof: sp_consensus_babe::EquivocationProof<
 						<Block as BlockT>::Header,