Rename Palette to FRAME (#4182)

* palette -> frame * PALETTE, Palette -> FRAME * Move folder pallete -> frame * Update docs/Structure.adoc Co-Authored-By: Benjamin Kampmann <ben.kampmann@googlemail.com> * Update docs/README.adoc Co-Authored-By: Benjamin Kampmann <ben.kampmann@googlemail.com> * Update README.adoc
2026-06-13 04:41:02 +00:00 · 2019-11-22 19:21:25 +01:00
parent 68351da29b
commit c9175b59ff
206 changed files with 485 additions and 483 deletions
@@ -0,0 +1,553 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Consensus extension module for BABE consensus. Collects on-chain randomness
+//! from VRF outputs and manages epoch transitions.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+#![forbid(unused_must_use, unsafe_code, unused_variables, unused_must_use)]
+#![deny(unused_imports)]
+pub use timestamp;
+use sp_timestamp;
+
+use rstd::{result, prelude::*};
+use support::{decl_storage, decl_module, traits::FindAuthor, traits::Get};
+use sp_timestamp::OnTimestampSet;
+use sr_primitives::{generic::DigestItem, ConsensusEngineId, Perbill};
+use sr_primitives::traits::{IsMember, SaturatedConversion, Saturating, RandomnessBeacon};
+use sr_staking_primitives::{
+	SessionIndex,
+	offence::{Offence, Kind},
+};
+
+use codec::{Encode, Decode};
+use inherents::{InherentIdentifier, InherentData, ProvideInherent, MakeFatalError};
+use babe_primitives::{
+	BABE_ENGINE_ID, ConsensusLog, BabeAuthorityWeight, NextEpochDescriptor, RawBabePreDigest,
+	SlotNumber, inherents::{INHERENT_IDENTIFIER, BabeInherentData}
+};
+pub use babe_primitives::{AuthorityId, VRF_OUTPUT_LENGTH, PUBLIC_KEY_LENGTH};
+
+#[cfg(all(feature = "std", test))]
+mod tests;
+
+#[cfg(all(feature = "std", test))]
+mod mock;
+
+pub trait Trait: timestamp::Trait {
+	/// The amount of time, in slots, that each epoch should last.
+	type EpochDuration: Get<SlotNumber>;
+
+	/// The expected average block time at which BABE should be creating
+	/// blocks. Since BABE is probabilistic it is not trivial to figure out
+	/// what the expected average block time should be based on the slot
+	/// duration and the security parameter `c` (where `1 - c` represents
+	/// the probability of a slot being empty).
+	type ExpectedBlockTime: Get<Self::Moment>;
+
+	/// BABE requires some logic to be triggered on every block to query for whether an epoch
+	/// has ended and to perform the transition to the next epoch.
+	///
+	/// Typically, the `ExternalTrigger` type should be used. An internal trigger should only be used
+	/// when no other module is responsible for changing authority set.
+	type EpochChangeTrigger: EpochChangeTrigger;
+}
+
+/// Trigger an epoch change, if any should take place.
+pub trait EpochChangeTrigger {
+	/// Trigger an epoch change, if any should take place. This should be called
+	/// during every block, after initialization is done.
+	fn trigger<T: Trait>(now: T::BlockNumber);
+}
+
+/// A type signifying to BABE that an external trigger
+/// for epoch changes (e.g. pallet-session) is used.
+pub struct ExternalTrigger;
+
+impl EpochChangeTrigger for ExternalTrigger {
+	fn trigger<T: Trait>(_: T::BlockNumber) { } // nothing - trigger is external.
+}
+
+/// A type signifying to BABE that it should perform epoch changes
+/// with an internal trigger, recycling the same authorities forever.
+pub struct SameAuthoritiesForever;
+
+impl EpochChangeTrigger for SameAuthoritiesForever {
+	fn trigger<T: Trait>(now: T::BlockNumber) {
+		if <Module<T>>::should_epoch_change(now) {
+			let authorities = <Module<T>>::authorities();
+			let next_authorities = authorities.clone();
+
+			<Module<T>>::enact_epoch_change(authorities, next_authorities);
+		}
+	}
+}
+
+/// The length of the BABE randomness
+pub const RANDOMNESS_LENGTH: usize = 32;
+
+const UNDER_CONSTRUCTION_SEGMENT_LENGTH: usize = 256;
+
+type MaybeVrf = Option<[u8; 32 /* VRF_OUTPUT_LENGTH */]>;
+
+decl_storage! {
+	trait Store for Module<T: Trait> as Babe {
+		/// Current epoch index.
+		pub EpochIndex get(fn epoch_index): u64;
+
+		/// Current epoch authorities.
+		pub Authorities get(fn authorities): Vec<(AuthorityId, BabeAuthorityWeight)>;
+
+		/// The slot at which the first epoch actually started. This is 0
+		/// until the first block of the chain.
+		pub GenesisSlot get(fn genesis_slot): u64;
+
+		/// Current slot number.
+		pub CurrentSlot get(fn current_slot): u64;
+
+		/// The epoch randomness for the *current* epoch.
+		///
+		/// # Security
+		///
+		/// This MUST NOT be used for gambling, as it can be influenced by a
+		/// malicious validator in the short term. It MAY be used in many
+		/// cryptographic protocols, however, so long as one remembers that this
+		/// (like everything else on-chain) it is public. For example, it can be
+		/// used where a number is needed that cannot have been chosen by an
+		/// adversary, for purposes such as public-coin zero-knowledge proofs.
+		// NOTE: the following fields don't use the constants to define the
+		// array size because the metadata API currently doesn't resolve the
+		// variable to its underlying value.
+		pub Randomness get(fn randomness): [u8; 32 /* RANDOMNESS_LENGTH */];
+
+		/// Next epoch randomness.
+		NextRandomness: [u8; 32 /* RANDOMNESS_LENGTH */];
+
+		/// Randomness under construction.
+		///
+		/// We make a tradeoff between storage accesses and list length.
+		/// We store the under-construction randomness in segments of up to
+		/// `UNDER_CONSTRUCTION_SEGMENT_LENGTH`.
+		///
+		/// Once a segment reaches this length, we begin the next one.
+		/// We reset all segments and return to `0` at the beginning of every
+		/// epoch.
+		SegmentIndex build(|_| 0): u32;
+		UnderConstruction: map u32 => Vec<[u8; 32 /* VRF_OUTPUT_LENGTH */]>;
+
+		/// Temporary value (cleared at block finalization) which is `Some`
+		/// if per-block initialization has already been called for current block.
+		Initialized get(fn initialized): Option<MaybeVrf>;
+	}
+	add_extra_genesis {
+		config(authorities): Vec<(AuthorityId, BabeAuthorityWeight)>;
+		build(|config| Module::<T>::initialize_authorities(&config.authorities))
+	}
+}
+
+decl_module! {
+	/// The BABE SRML module
+	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+		/// The number of **slots** that an epoch takes. We couple sessions to
+		/// epochs, i.e. we start a new session once the new epoch begins.
+		const EpochDuration: u64 = T::EpochDuration::get();
+
+		/// The expected average block time at which BABE should be creating
+		/// blocks. Since BABE is probabilistic it is not trivial to figure out
+		/// what the expected average block time should be based on the slot
+		/// duration and the security parameter `c` (where `1 - c` represents
+		/// the probability of a slot being empty).
+		const ExpectedBlockTime: T::Moment = T::ExpectedBlockTime::get();
+
+		/// Initialization
+		fn on_initialize(now: T::BlockNumber) {
+			Self::do_initialize(now);
+		}
+
+		/// Block finalization
+		fn on_finalize() {
+			// at the end of the block, we can safely include the new VRF output
+			// from this block into the under-construction randomness. If we've determined
+			// that this block was the first in a new epoch, the changeover logic has
+			// already occurred at this point, so the under-construction randomness
+			// will only contain outputs from the right epoch.
+			if let Some(Some(vrf_output)) = Initialized::take() {
+				Self::deposit_vrf_output(&vrf_output);
+			}
+		}
+	}
+}
+
+impl<T: Trait> RandomnessBeacon for Module<T> {
+	fn random() -> [u8; VRF_OUTPUT_LENGTH] {
+		Self::randomness()
+	}
+}
+
+/// A BABE public key
+pub type BabeKey = [u8; PUBLIC_KEY_LENGTH];
+
+impl<T: Trait> FindAuthor<u32> for Module<T> {
+	fn find_author<'a, I>(digests: I) -> Option<u32> where
+		I: 'a + IntoIterator<Item=(ConsensusEngineId, &'a [u8])>
+	{
+		for (id, mut data) in digests.into_iter() {
+			if id == BABE_ENGINE_ID {
+				let pre_digest = RawBabePreDigest::decode(&mut data).ok()?;
+				return Some(match pre_digest {
+					RawBabePreDigest::Primary { authority_index, .. } =>
+						authority_index,
+					RawBabePreDigest::Secondary { authority_index, .. } =>
+						authority_index,
+				});
+			}
+		}
+
+		return None;
+	}
+}
+
+impl<T: Trait> IsMember<AuthorityId> for Module<T> {
+	fn is_member(authority_id: &AuthorityId) -> bool {
+		<Module<T>>::authorities()
+			.iter()
+			.any(|id| &id.0 == authority_id)
+	}
+}
+
+impl<T: Trait> session::ShouldEndSession<T::BlockNumber> for Module<T> {
+	fn should_end_session(now: T::BlockNumber) -> bool {
+		// it might be (and it is in current implementation) that session module is calling
+		// should_end_session() from it's own on_initialize() handler
+		// => because session on_initialize() is called earlier than ours, let's ensure
+		// that we have synced with digest before checking if session should be ended.
+		Self::do_initialize(now);
+
+		Self::should_epoch_change(now)
+	}
+}
+
+// TODO [slashing]: @marcio use this, remove the dead_code annotation.
+/// A BABE equivocation offence report.
+///
+/// When a validator released two or more blocks at the same slot.
+#[allow(dead_code)]
+struct BabeEquivocationOffence<FullIdentification> {
+	/// A babe slot number in which this incident happened.
+	slot: u64,
+	/// The session index in which the incident happened.
+	session_index: SessionIndex,
+	/// The size of the validator set at the time of the offence.
+	validator_set_count: u32,
+	/// The authority that produced the equivocation.
+	offender: FullIdentification,
+}
+
+impl<FullIdentification: Clone> Offence<FullIdentification> for BabeEquivocationOffence<FullIdentification> {
+	const ID: Kind = *b"babe:equivocatio";
+	type TimeSlot = u64;
+
+	fn offenders(&self) -> Vec<FullIdentification> {
+		vec![self.offender.clone()]
+	}
+
+	fn session_index(&self) -> SessionIndex {
+		self.session_index
+	}
+
+	fn validator_set_count(&self) -> u32 {
+		self.validator_set_count
+	}
+
+	fn time_slot(&self) -> Self::TimeSlot {
+		self.slot
+	}
+
+	fn slash_fraction(
+		offenders_count: u32,
+		validator_set_count: u32,
+	) -> Perbill {
+		// the formula is min((3k / n)^2, 1)
+		let x = Perbill::from_rational_approximation(3 * offenders_count, validator_set_count);
+		// _ ^ 2
+		x.square()
+	}
+}
+
+impl<T: Trait> Module<T> {
+	/// Determine the BABE slot duration based on the Timestamp module configuration.
+	pub fn slot_duration() -> T::Moment {
+		// we double the minimum block-period so each author can always propose within
+		// the majority of their slot.
+		<T as timestamp::Trait>::MinimumPeriod::get().saturating_mul(2.into())
+	}
+
+	/// Determine whether an epoch change should take place at this block.
+	/// Assumes that initialization has already taken place.
+	pub fn should_epoch_change(now: T::BlockNumber) -> bool {
+		// The epoch has technically ended during the passage of time
+		// between this block and the last, but we have to "end" the epoch now,
+		// since there is no earlier possible block we could have done it.
+		//
+		// The exception is for block 1: the genesis has slot 0, so we treat
+		// epoch 0 as having started at the slot of block 1. We want to use
+		// the same randomness and validator set as signalled in the genesis,
+		// so we don't rotate the epoch.
+		now != sr_primitives::traits::One::one() && {
+			let diff = CurrentSlot::get().saturating_sub(Self::current_epoch_start());
+			diff >= T::EpochDuration::get()
+		}
+	}
+
+	/// DANGEROUS: Enact an epoch change. Should be done on every block where `should_epoch_change` has returned `true`,
+	/// and the caller is the only caller of this function.
+	///
+	/// Typically, this is not handled directly by the user, but by higher-level validator-set manager logic like
+	/// `pallet-session`.
+	pub fn enact_epoch_change(
+		authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
+		next_authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
+	) {
+		// PRECONDITION: caller has done initialization and is guaranteed
+		// by the session module to be called before this.
+		#[cfg(debug_assertions)]
+		{
+			assert!(Self::initialized().is_some())
+		}
+
+		// Update epoch index
+		let epoch_index = EpochIndex::get()
+			.checked_add(1)
+			.expect("epoch indices will never reach 2^64 before the death of the universe; qed");
+
+		EpochIndex::put(epoch_index);
+		Authorities::put(authorities);
+
+		// Update epoch randomness.
+		let next_epoch_index = epoch_index
+			.checked_add(1)
+			.expect("epoch indices will never reach 2^64 before the death of the universe; qed");
+
+		// Returns randomness for the current epoch and computes the *next*
+		// epoch randomness.
+		let randomness = Self::randomness_change_epoch(next_epoch_index);
+		Randomness::put(randomness);
+
+		// 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 = NextEpochDescriptor {
+			authorities: next_authorities,
+			randomness: next_randomness,
+		};
+
+		Self::deposit_consensus(ConsensusLog::NextEpochData(next))
+	}
+
+	// finds the start slot of the current epoch. only guaranteed to
+	// give correct results after `do_initialize` of the first block
+	// in the chain (as its result is based off of `GenesisSlot`).
+	fn current_epoch_start() -> SlotNumber {
+		(EpochIndex::get() * T::EpochDuration::get()) + GenesisSlot::get()
+	}
+
+	fn deposit_consensus<U: Encode>(new: U) {
+		let log: DigestItem<T::Hash> = DigestItem::Consensus(BABE_ENGINE_ID, new.encode());
+		<system::Module<T>>::deposit_log(log.into())
+	}
+
+	fn deposit_vrf_output(vrf_output: &[u8; VRF_OUTPUT_LENGTH]) {
+		let segment_idx = <SegmentIndex>::get();
+		let mut segment = <UnderConstruction>::get(&segment_idx);
+		if segment.len() < UNDER_CONSTRUCTION_SEGMENT_LENGTH {
+			// push onto current segment: not full.
+			segment.push(*vrf_output);
+			<UnderConstruction>::insert(&segment_idx, &segment);
+		} else {
+			// move onto the next segment and update the index.
+			let segment_idx = segment_idx + 1;
+			<UnderConstruction>::insert(&segment_idx, &vec![*vrf_output]);
+			<SegmentIndex>::put(&segment_idx);
+		}
+	}
+
+	fn do_initialize(now: T::BlockNumber) {
+		// since do_initialize can be called twice (if session module is present)
+		// => let's ensure that we only modify the storage once per block
+		let initialized = Self::initialized().is_some();
+		if initialized {
+			return;
+		}
+
+		let maybe_pre_digest = <system::Module<T>>::digest()
+			.logs
+			.iter()
+			.filter_map(|s| s.as_pre_runtime())
+			.filter_map(|(id, mut data)| if id == BABE_ENGINE_ID {
+				RawBabePreDigest::decode(&mut data).ok()
+			} else {
+				None
+			})
+			.next();
+
+		let maybe_vrf = maybe_pre_digest.and_then(|digest| {
+			// on the first non-zero block (i.e. block #1)
+			// this is where the first epoch (epoch #0) actually starts.
+			// we need to adjust internal storage accordingly.
+			if GenesisSlot::get() == 0 {
+				GenesisSlot::put(digest.slot_number());
+				debug_assert_ne!(GenesisSlot::get(), 0);
+
+				// deposit a log because this is the first block in epoch #0
+				// we use the same values as genesis because we haven't collected any
+				// randomness yet.
+				let next = NextEpochDescriptor {
+					authorities: Self::authorities(),
+					randomness: Self::randomness(),
+				};
+
+				Self::deposit_consensus(ConsensusLog::NextEpochData(next))
+			}
+
+			CurrentSlot::put(digest.slot_number());
+
+			if let RawBabePreDigest::Primary { vrf_output, .. } = digest {
+				// place the VRF output into the `Initialized` storage item
+				// and it'll be put onto the under-construction randomness
+				// later, once we've decided which epoch this block is in.
+				Some(vrf_output)
+			} else {
+				None
+			}
+		});
+
+		Initialized::put(maybe_vrf);
+
+		// enact epoch change, if necessary.
+		T::EpochChangeTrigger::trigger::<T>(now)
+	}
+
+	/// Call this function exactly once when an epoch changes, to update the
+	/// randomness. Returns the new randomness.
+	fn randomness_change_epoch(next_epoch_index: u64) -> [u8; RANDOMNESS_LENGTH] {
+		let this_randomness = NextRandomness::get();
+		let segment_idx: u32 = <SegmentIndex>::mutate(|s| rstd::mem::replace(s, 0));
+
+		// overestimate to the segment being full.
+		let rho_size = segment_idx.saturating_add(1) as usize * UNDER_CONSTRUCTION_SEGMENT_LENGTH;
+
+		let next_randomness = compute_randomness(
+			this_randomness,
+			next_epoch_index,
+			(0..segment_idx).flat_map(|i| <UnderConstruction>::take(&i)),
+			Some(rho_size),
+		);
+		NextRandomness::put(&next_randomness);
+		this_randomness
+	}
+
+	fn initialize_authorities(authorities: &[(AuthorityId, BabeAuthorityWeight)]) {
+		if !authorities.is_empty() {
+			assert!(Authorities::get().is_empty(), "Authorities are already initialized!");
+			Authorities::put(authorities);
+		}
+	}
+}
+
+impl<T: Trait> OnTimestampSet<T::Moment> for Module<T> {
+	fn on_timestamp_set(_moment: T::Moment) { }
+}
+
+impl<T: Trait> sr_primitives::BoundToRuntimeAppPublic for Module<T> {
+	type Public = AuthorityId;
+}
+
+impl<T: Trait> session::OneSessionHandler<T::AccountId> for Module<T> {
+	type Key = AuthorityId;
+
+	fn on_genesis_session<'a, I: 'a>(validators: I)
+		where I: Iterator<Item=(&'a T::AccountId, AuthorityId)>
+	{
+		let authorities = validators.map(|(_, k)| (k, 1)).collect::<Vec<_>>();
+		Self::initialize_authorities(&authorities);
+	}
+
+	fn on_new_session<'a, I: 'a>(_changed: bool, validators: I, queued_validators: I)
+		where I: Iterator<Item=(&'a T::AccountId, AuthorityId)>
+	{
+		let authorities = validators.map(|(_account, k)| {
+			(k, 1)
+		}).collect::<Vec<_>>();
+
+		let next_authorities = queued_validators.map(|(_account, k)| {
+			(k, 1)
+		}).collect::<Vec<_>>();
+
+		Self::enact_epoch_change(authorities, next_authorities)
+	}
+
+	fn on_disabled(i: usize) {
+		Self::deposit_consensus(ConsensusLog::OnDisabled(i as u32))
+	}
+}
+
+// compute randomness for a new epoch. rho is the concatenation of all
+// VRF outputs in the prior epoch.
+//
+// an optional size hint as to how many VRF outputs there were may be provided.
+fn compute_randomness(
+	last_epoch_randomness: [u8; RANDOMNESS_LENGTH],
+	epoch_index: u64,
+	rho: impl Iterator<Item=[u8; VRF_OUTPUT_LENGTH]>,
+	rho_size_hint: Option<usize>,
+) -> [u8; RANDOMNESS_LENGTH] {
+	let mut s = Vec::with_capacity(40 + rho_size_hint.unwrap_or(0) * VRF_OUTPUT_LENGTH);
+	s.extend_from_slice(&last_epoch_randomness);
+	s.extend_from_slice(&epoch_index.to_le_bytes());
+
+	for vrf_output in rho {
+		s.extend_from_slice(&vrf_output[..]);
+	}
+
+	runtime_io::hashing::blake2_256(&s)
+}
+
+impl<T: Trait> ProvideInherent for Module<T> {
+	type Call = timestamp::Call<T>;
+	type Error = MakeFatalError<inherents::Error>;
+	const INHERENT_IDENTIFIER: InherentIdentifier = INHERENT_IDENTIFIER;
+
+	fn create_inherent(_: &InherentData) -> Option<Self::Call> {
+		None
+	}
+
+	fn check_inherent(call: &Self::Call, data: &InherentData) -> result::Result<(), Self::Error> {
+		let timestamp = match call {
+			timestamp::Call::set(ref timestamp) => timestamp.clone(),
+			_ => return Ok(()),
+		};
+
+		let timestamp_based_slot = (timestamp / Self::slot_duration()).saturated_into::<u64>();
+		let seal_slot = data.babe_inherent_data()?;
+
+		if timestamp_based_slot == seal_slot {
+			Ok(())
+		} else {
+			Err(inherents::Error::from("timestamp set in block doesn't match slot in seal").into())
+		}
+	}
+}
@@ -0,0 +1,109 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Test utilities
+#![allow(dead_code, unused_imports)]
+
+use super::{Trait, Module, GenesisConfig};
+use babe_primitives::AuthorityId;
+use sr_primitives::{
+	traits::IdentityLookup, Perbill, testing::{Header, UintAuthorityId}, impl_opaque_keys,
+};
+use sr_version::RuntimeVersion;
+use support::{impl_outer_origin, parameter_types};
+use runtime_io;
+use primitives::{H256, Blake2Hasher};
+
+impl_outer_origin!{
+	pub enum Origin for Test {}
+}
+
+type DummyValidatorId = u64;
+
+// Workaround for https://github.com/rust-lang/rust/issues/26925 . Remove when sorted.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct Test;
+
+parameter_types! {
+	pub const BlockHashCount: u64 = 250;
+	pub const MaximumBlockWeight: u32 = 1024;
+	pub const MaximumBlockLength: u32 = 2 * 1024;
+	pub const AvailableBlockRatio: Perbill = Perbill::one();
+	pub const MinimumPeriod: u64 = 1;
+	pub const EpochDuration: u64 = 3;
+	pub const ExpectedBlockTime: u64 = 1;
+	pub const Version: RuntimeVersion = test_runtime::VERSION;
+	pub const DisabledValidatorsThreshold: Perbill = Perbill::from_percent(16);
+}
+
+impl system::Trait for Test {
+	type Origin = Origin;
+	type Index = u64;
+	type BlockNumber = u64;
+	type Call = ();
+	type Hash = H256;
+	type Version = Version;
+	type Hashing = sr_primitives::traits::BlakeTwo256;
+	type AccountId = DummyValidatorId;
+	type Lookup = IdentityLookup<Self::AccountId>;
+	type Header = Header;
+	type Event = ();
+	type BlockHashCount = BlockHashCount;
+	type MaximumBlockWeight = MaximumBlockWeight;
+	type AvailableBlockRatio = AvailableBlockRatio;
+	type MaximumBlockLength = MaximumBlockLength;
+}
+
+impl_opaque_keys! {
+	pub struct MockSessionKeys {
+		pub dummy: UintAuthorityId,
+	}
+}
+
+impl session::Trait for Test {
+	type Event = ();
+	type ValidatorId = <Self as system::Trait>::AccountId;
+	type ShouldEndSession = Babe;
+	type SessionHandler = (Babe,Babe,);
+	type OnSessionEnding = ();
+	type ValidatorIdOf = ();
+	type SelectInitialValidators = ();
+	type Keys = MockSessionKeys;
+	type DisabledValidatorsThreshold = DisabledValidatorsThreshold;
+}
+
+impl timestamp::Trait for Test {
+	type Moment = u64;
+	type OnTimestampSet = Babe;
+	type MinimumPeriod = MinimumPeriod;
+}
+
+impl Trait for Test {
+	type EpochDuration = EpochDuration;
+	type ExpectedBlockTime = ExpectedBlockTime;
+	type EpochChangeTrigger = crate::ExternalTrigger;
+}
+
+pub fn new_test_ext(authorities: Vec<DummyValidatorId>) -> runtime_io::TestExternalities {
+	let mut t = system::GenesisConfig::default().build_storage::<Test>().unwrap();
+	GenesisConfig {
+		authorities: authorities.into_iter().map(|a| (UintAuthorityId(a).to_public_key(), 1)).collect(),
+	}.assimilate_storage::<Test>(&mut t).unwrap();
+	t.into()
+}
+
+pub type System = system::Module<Test>;
+pub type Babe = Module<Test>;
@@ -0,0 +1,126 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Consensus extension module tests for BABE consensus.
+
+use super::*;
+use mock::{new_test_ext, Babe, Test};
+use sr_primitives::{traits::OnFinalize, testing::{Digest, DigestItem}};
+use session::ShouldEndSession;
+
+const EMPTY_RANDOMNESS: [u8; 32] = [
+	74, 25, 49, 128, 53, 97, 244, 49,
+	222, 202, 176, 2, 231, 66, 95, 10,
+	133, 49, 213, 228, 86, 161, 164, 127,
+	217, 153, 138, 37, 48, 192, 248, 0,
+];
+
+fn make_pre_digest(
+	authority_index: babe_primitives::AuthorityIndex,
+	slot_number: babe_primitives::SlotNumber,
+	vrf_output: [u8; babe_primitives::VRF_OUTPUT_LENGTH],
+	vrf_proof: [u8; babe_primitives::VRF_PROOF_LENGTH],
+) -> Digest {
+	let digest_data = babe_primitives::RawBabePreDigest::Primary {
+		authority_index,
+		slot_number,
+		vrf_output,
+		vrf_proof,
+	};
+	let log = DigestItem::PreRuntime(babe_primitives::BABE_ENGINE_ID, digest_data.encode());
+	Digest { logs: vec![log] }
+}
+
+#[test]
+fn empty_randomness_is_correct() {
+	let s = compute_randomness([0; RANDOMNESS_LENGTH], 0, std::iter::empty(), None);
+	assert_eq!(s, EMPTY_RANDOMNESS);
+}
+
+#[test]
+fn initial_values() {
+	new_test_ext(vec![0, 1, 2, 3]).execute_with(|| {
+		assert_eq!(Babe::authorities().len(), 4)
+	})
+}
+
+#[test]
+fn check_module() {
+	new_test_ext(vec![0, 1, 2, 3]).execute_with(|| {
+		assert!(!Babe::should_end_session(0), "Genesis does not change sessions");
+		assert!(!Babe::should_end_session(200000),
+			"BABE does not include the block number in epoch calculations");
+	})
+}
+
+type System = system::Module<Test>;
+
+#[test]
+fn first_block_epoch_zero_start() {
+	new_test_ext(vec![0, 1, 2, 3]).execute_with(|| {
+		let genesis_slot = 100;
+		let first_vrf = [1; 32];
+		let pre_digest = make_pre_digest(
+			0,
+			genesis_slot,
+			first_vrf,
+			[0xff; 64],
+		);
+
+		assert_eq!(Babe::genesis_slot(), 0);
+		System::initialize(&1, &Default::default(), &Default::default(), &pre_digest);
+
+		// see implementation of the function for details why: we issue an
+		// epoch-change digest but don't do it via the normal session mechanism.
+		assert!(!Babe::should_end_session(1));
+		assert_eq!(Babe::genesis_slot(), genesis_slot);
+		assert_eq!(Babe::current_slot(), genesis_slot);
+		assert_eq!(Babe::epoch_index(), 0);
+
+		Babe::on_finalize(1);
+		let header = System::finalize();
+
+		assert_eq!(SegmentIndex::get(), 0);
+		assert_eq!(UnderConstruction::get(0), vec![first_vrf]);
+		assert_eq!(Babe::randomness(), [0; 32]);
+		assert_eq!(NextRandomness::get(), [0; 32]);
+
+		assert_eq!(header.digest.logs.len(), 2);
+		assert_eq!(pre_digest.logs.len(), 1);
+		assert_eq!(header.digest.logs[0], pre_digest.logs[0]);
+
+		let authorities = Babe::authorities();
+		let consensus_log = babe_primitives::ConsensusLog::NextEpochData(
+			babe_primitives::NextEpochDescriptor {
+				authorities,
+				randomness: Babe::randomness(),
+			}
+		);
+		let consensus_digest = DigestItem::Consensus(BABE_ENGINE_ID, consensus_log.encode());
+
+		// first epoch descriptor has same info as last.
+		assert_eq!(header.digest.logs[1], consensus_digest.clone())
+	})
+}
+
+#[test]
+fn authority_index() {
+	new_test_ext(vec![0, 1, 2, 3]).execute_with(|| {
+		assert_eq!(
+			Babe::find_author((&[(BABE_ENGINE_ID, &[][..])]).into_iter().cloned()), None,
+			"Trivially invalid authorities are ignored")
+	})
+}