Fixing BABE epochs to change between blocks (#3583)

* always fetch epoch from runtime

* node integration tests don't test light nodes

* give stand-in full node a FULL role

* rejig babe APIs

* introduce next-epoch-descriptor type

* overhaul srml-BABE epoch logic

* ensure VRF outputs end up in the right epoch-randomness

* rewrite `do_initialize` to remove unnecessary loop

* begin accounting for next epoch in epoch function

* slots passes header to epoch_data

* pass slot_number to SlotWorker::epoch_data

* begin extracting epoch-change logic into its own module

* aux methods for block weight

* aux methods for genesis configuration

* comment-out most, refactor header-check pipeline

* mostly flesh out verifier again

* reinstantiate babe BlockImport implementation

* reinstate import-queue instantiation

* reintroduce slot-worker implementation

* reinstate pretty much all the rest

* move fork-choice logic to BlockImport

* fix some, but not all errors

* patch test-runtime

* make is_descendent of slightly more generic

* get skeleton compiling when passing is_descendent_of

* make descendent-of-builder more succinct

* restore ordering of authority_index / slot_number

* start fiddling with tests

* fix warnings

* improve initialization architecture and handle genesis

* tests use correct block-import

* fix BABE tests

* fix some compiler errors

* fix node-cli compilation

* all crates compile

* bump runtime versions and fix some warnings

* tweak fork-tree search implementation

* do backtracking search in fork-tree

* node-cli integration tests now work

* fix broken assumption in test_connectivity

* babe tests fail for the right reasons.

* test genesis epoch logic for epoch_changes

* test that epochs can change between blocks

* First BABE SRML test

* Testing infrastructure for BABE

Also includes a trivial additional test.

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* A little more test progress

* More work on BABE testing

* Try to get the tests working

* Implement `UintAuthorityId`-based test mocks

* Fix compilation errors

* Adjust to upstream changes

* Block numbers are ignored in BABE epoch calculation

* authority_index() should ignore invalid authorities

* Fix compile error

* Add tests that session transitions happen

* Check if BABE produces logs

It currently does not.

* Fix test suite

This was really nasty, due to a type confusion that showed up as an
off-by-1 buffer error.

* Add additional tests

Most of these were derived from the current output, so they are only
useful to guard against regressions.

* Make the tests more readable

Also bump impl_version.

* Fix excessive line width

* Remove unused imports

* Update srml/babe/src/lib.rs

Co-Authored-By: André Silva <andre.beat@gmail.com>

* try to fix imports

* Fix build errors in test suite

* tests did not pass

* Try to get at least one digest to be output

Currently, the code emits either no digests (if I don’t call
`Session::rotate_session()` or two digests (if I do), which is wrong.

* More tests

They still don’t work, but this should help debugging.

* fix silly error

* Don’t even try to compile a broken test

* remove broken check_epoch test and add one for genesis epoch

* Check that the length of the pre-digests is correct

* Bump `impl_version`

* use epoch_for_descendent_of even for genesis

* account for competing block 1s

* finish srml-babe docs

Co-Authored-By: André Silva <andre.beat@gmail.com>

* address grumbles

substrate/srml/babe/src/tests.rs

@@ -0,0 +1,127 @@
+// 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 runtime_io::with_externalities;
+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() {
+	with_externalities(&mut new_test_ext(vec![0, 1, 2, 3]), || {
+		assert_eq!(Babe::authorities().len(), 4)
+	})
+}
+
+#[test]
+fn check_module() {
+	with_externalities(&mut new_test_ext(vec![0, 1, 2, 3]), || {
+		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() {
+	with_externalities(&mut new_test_ext(vec![0, 1, 2, 3]), || {
+		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() {
+	with_externalities(&mut new_test_ext(vec![0, 1, 2, 3]), || {
+		assert_eq!(
+			Babe::find_author((&[(BABE_ENGINE_ID, &[][..])]).into_iter().cloned()), None,
+			"Trivially invalid authorities are ignored")
+	})
+}