1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program 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.

// This program 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 this program. If not, see <https://www.gnu.org/licenses/>.

use std::{collections::HashMap, marker::PhantomData, sync::Arc};

use log::debug;
use parity_scale_codec::Decode;

use sc_client_api::{backend::Backend, utils::is_descendent_of};
use sc_consensus::{
	shared_data::{SharedDataLocked, SharedDataLockedUpgradable},
	BlockCheckParams, BlockImport, BlockImportParams, ImportResult, JustificationImport,
};
use sc_telemetry::TelemetryHandle;
use sc_utils::mpsc::TracingUnboundedSender;
use sp_api::{Core, RuntimeApiInfo};
use sp_blockchain::BlockStatus;
use sp_consensus::{BlockOrigin, Error as ConsensusError, SelectChain};
use sp_consensus_grandpa::{ConsensusLog, GrandpaApi, ScheduledChange, SetId, GRANDPA_ENGINE_ID};
use sp_core::hashing::twox_128;
use sp_runtime::{
	generic::OpaqueDigestItemId,
	traits::{Block as BlockT, Header as HeaderT, NumberFor, Zero},
	Justification,
};

use crate::{
	authorities::{AuthoritySet, DelayKind, PendingChange, SharedAuthoritySet},
	environment,
	justification::GrandpaJustification,
	notification::GrandpaJustificationSender,
	AuthoritySetChanges, ClientForGrandpa, CommandOrError, Error, NewAuthoritySet, VoterCommand,
	LOG_TARGET,
};

/// A block-import handler for GRANDPA.
///
/// This scans each imported block for signals of changing authority set.
/// If the block being imported enacts an authority set change then:
/// - If the current authority set is still live: we import the block
/// - Otherwise, the block must include a valid justification.
///
/// When using GRANDPA, the block import worker should be using this block import
/// object.
pub struct GrandpaBlockImport<Backend, Block: BlockT, Client, SC> {
	inner: Arc<Client>,
	justification_import_period: u32,
	select_chain: SC,
	authority_set: SharedAuthoritySet<Block::Hash, NumberFor<Block>>,
	send_voter_commands: TracingUnboundedSender<VoterCommand<Block::Hash, NumberFor<Block>>>,
	authority_set_hard_forks: HashMap<Block::Hash, PendingChange<Block::Hash, NumberFor<Block>>>,
	justification_sender: GrandpaJustificationSender<Block>,
	telemetry: Option<TelemetryHandle>,
	_phantom: PhantomData<Backend>,
}

impl<Backend, Block: BlockT, Client, SC: Clone> Clone
	for GrandpaBlockImport<Backend, Block, Client, SC>
{
	fn clone(&self) -> Self {
		GrandpaBlockImport {
			inner: self.inner.clone(),
			justification_import_period: self.justification_import_period,
			select_chain: self.select_chain.clone(),
			authority_set: self.authority_set.clone(),
			send_voter_commands: self.send_voter_commands.clone(),
			authority_set_hard_forks: self.authority_set_hard_forks.clone(),
			justification_sender: self.justification_sender.clone(),
			telemetry: self.telemetry.clone(),
			_phantom: PhantomData,
		}
	}
}

#[async_trait::async_trait]
impl<BE, Block: BlockT, Client, SC> JustificationImport<Block>
	for GrandpaBlockImport<BE, Block, Client, SC>
where
	NumberFor<Block>: finality_grandpa::BlockNumberOps,
	BE: Backend<Block>,
	Client: ClientForGrandpa<Block, BE>,
	SC: SelectChain<Block>,
{
	type Error = ConsensusError;

	async fn on_start(&mut self) -> Vec<(Block::Hash, NumberFor<Block>)> {
		let mut out = Vec::new();
		let chain_info = self.inner.info();

		// request justifications for all pending changes for which change blocks have already been
		// imported
		let pending_changes: Vec<_> =
			self.authority_set.inner().pending_changes().cloned().collect();

		for pending_change in pending_changes {
			if pending_change.delay_kind == DelayKind::Finalized &&
				pending_change.effective_number() > chain_info.finalized_number &&
				pending_change.effective_number() <= chain_info.best_number
			{
				let effective_block_hash = if !pending_change.delay.is_zero() {
					self.select_chain
						.finality_target(
							pending_change.canon_hash,
							Some(pending_change.effective_number()),
						)
						.await
				} else {
					Ok(pending_change.canon_hash)
				};

				if let Ok(hash) = effective_block_hash {
					if let Ok(Some(header)) = self.inner.header(hash) {
						if *header.number() == pending_change.effective_number() {
							out.push((header.hash(), *header.number()));
						}
					}
				}
			}
		}

		out
	}

	async fn import_justification(
		&mut self,
		hash: Block::Hash,
		number: NumberFor<Block>,
		justification: Justification,
	) -> Result<(), Self::Error> {
		// this justification was requested by the sync service, therefore we
		// are not sure if it should enact a change or not. it could have been a
		// request made as part of initial sync but that means the justification
		// wasn't part of the block and was requested asynchronously, probably
		// makes sense to log in that case.
		GrandpaBlockImport::import_justification(self, hash, number, justification, false, false)
	}
}

enum AppliedChanges<H, N> {
	Standard(bool), // true if the change is ready to be applied (i.e. it's a root)
	Forced(NewAuthoritySet<H, N>),
	None,
}

impl<H, N> AppliedChanges<H, N> {
	fn needs_justification(&self) -> bool {
		match *self {
			AppliedChanges::Standard(_) => true,
			AppliedChanges::Forced(_) | AppliedChanges::None => false,
		}
	}
}

struct PendingSetChanges<Block: BlockT> {
	just_in_case: Option<(
		AuthoritySet<Block::Hash, NumberFor<Block>>,
		SharedDataLockedUpgradable<AuthoritySet<Block::Hash, NumberFor<Block>>>,
	)>,
	applied_changes: AppliedChanges<Block::Hash, NumberFor<Block>>,
	do_pause: bool,
}

impl<Block: BlockT> PendingSetChanges<Block> {
	// revert the pending set change explicitly.
	fn revert(self) {}

	fn defuse(mut self) -> (AppliedChanges<Block::Hash, NumberFor<Block>>, bool) {
		self.just_in_case = None;
		let applied_changes = std::mem::replace(&mut self.applied_changes, AppliedChanges::None);
		(applied_changes, self.do_pause)
	}
}

impl<Block: BlockT> Drop for PendingSetChanges<Block> {
	fn drop(&mut self) {
		if let Some((old_set, mut authorities)) = self.just_in_case.take() {
			*authorities.upgrade() = old_set;
		}
	}
}

/// Checks the given header for a consensus digest signalling a **standard** scheduled change and
/// extracts it.
pub fn find_scheduled_change<B: BlockT>(
	header: &B::Header,
) -> Option<ScheduledChange<NumberFor<B>>> {
	let id = OpaqueDigestItemId::Consensus(&GRANDPA_ENGINE_ID);

	let filter_log = |log: ConsensusLog<NumberFor<B>>| match log {
		ConsensusLog::ScheduledChange(change) => Some(change),
		_ => None,
	};

	// find the first consensus digest with the right ID which converts to
	// the right kind of consensus log.
	header.digest().convert_first(|l| l.try_to(id).and_then(filter_log))
}

/// Checks the given header for a consensus digest signalling a **forced** scheduled change and
/// extracts it.
pub fn find_forced_change<B: BlockT>(
	header: &B::Header,
) -> Option<(NumberFor<B>, ScheduledChange<NumberFor<B>>)> {
	let id = OpaqueDigestItemId::Consensus(&GRANDPA_ENGINE_ID);

	let filter_log = |log: ConsensusLog<NumberFor<B>>| match log {
		ConsensusLog::ForcedChange(delay, change) => Some((delay, change)),
		_ => None,
	};

	// find the first consensus digest with the right ID which converts to
	// the right kind of consensus log.
	header.digest().convert_first(|l| l.try_to(id).and_then(filter_log))
}

impl<BE, Block: BlockT, Client, SC> GrandpaBlockImport<BE, Block, Client, SC>
where
	NumberFor<Block>: finality_grandpa::BlockNumberOps,
	BE: Backend<Block>,
	Client: ClientForGrandpa<Block, BE>,
	Client::Api: GrandpaApi<Block>,
	for<'a> &'a Client: BlockImport<Block, Error = ConsensusError>,
{
	// check for a new authority set change.
	fn check_new_change(
		&self,
		header: &Block::Header,
		hash: Block::Hash,
	) -> Option<PendingChange<Block::Hash, NumberFor<Block>>> {
		// check for forced authority set hard forks
		if let Some(change) = self.authority_set_hard_forks.get(&hash) {
			return Some(change.clone())
		}

		// check for forced change.
		if let Some((median_last_finalized, change)) = find_forced_change::<Block>(header) {
			return Some(PendingChange {
				next_authorities: change.next_authorities,
				delay: change.delay,
				canon_height: *header.number(),
				canon_hash: hash,
				delay_kind: DelayKind::Best { median_last_finalized },
			})
		}

		// check normal scheduled change.
		let change = find_scheduled_change::<Block>(header)?;
		Some(PendingChange {
			next_authorities: change.next_authorities,
			delay: change.delay,
			canon_height: *header.number(),
			canon_hash: hash,
			delay_kind: DelayKind::Finalized,
		})
	}

	fn make_authorities_changes(
		&self,
		block: &mut BlockImportParams<Block>,
		hash: Block::Hash,
		initial_sync: bool,
	) -> Result<PendingSetChanges<Block>, ConsensusError> {
		// when we update the authorities, we need to hold the lock
		// until the block is written to prevent a race if we need to restore
		// the old authority set on error or panic.
		struct InnerGuard<'a, H, N> {
			old: Option<AuthoritySet<H, N>>,
			guard: Option<SharedDataLocked<'a, AuthoritySet<H, N>>>,
		}

		impl<'a, H, N> InnerGuard<'a, H, N> {
			fn as_mut(&mut self) -> &mut AuthoritySet<H, N> {
				self.guard.as_mut().expect("only taken on deconstruction; qed")
			}

			fn set_old(&mut self, old: AuthoritySet<H, N>) {
				if self.old.is_none() {
					// ignore "newer" old changes.
					self.old = Some(old);
				}
			}

			fn consume(
				mut self,
			) -> Option<(AuthoritySet<H, N>, SharedDataLocked<'a, AuthoritySet<H, N>>)> {
				self.old
					.take()
					.map(|old| (old, self.guard.take().expect("only taken on deconstruction; qed")))
			}
		}

		impl<'a, H, N> Drop for InnerGuard<'a, H, N> {
			fn drop(&mut self) {
				if let (Some(mut guard), Some(old)) = (self.guard.take(), self.old.take()) {
					*guard = old;
				}
			}
		}

		let number = *(block.header.number());
		let maybe_change = self.check_new_change(&block.header, hash);

		// returns a function for checking whether a block is a descendent of another
		// consistent with querying client directly after importing the block.
		let parent_hash = *block.header.parent_hash();
		let is_descendent_of = is_descendent_of(&*self.inner, Some((hash, parent_hash)));

		let mut guard = InnerGuard { guard: Some(self.authority_set.inner_locked()), old: None };

		// whether to pause the old authority set -- happens after import
		// of a forced change block.
		let mut do_pause = false;

		// add any pending changes.
		if let Some(change) = maybe_change {
			let old = guard.as_mut().clone();
			guard.set_old(old);

			if let DelayKind::Best { .. } = change.delay_kind {
				do_pause = true;
			}

			guard
				.as_mut()
				.add_pending_change(change, &is_descendent_of)
				.map_err(|e| ConsensusError::ClientImport(e.to_string()))?;
		}

		let applied_changes = {
			let forced_change_set = guard
				.as_mut()
				.apply_forced_changes(
					hash,
					number,
					&is_descendent_of,
					initial_sync,
					self.telemetry.clone(),
				)
				.map_err(|e| ConsensusError::ClientImport(e.to_string()))
				.map_err(ConsensusError::from)?;

			if let Some((median_last_finalized_number, new_set)) = forced_change_set {
				let new_authorities = {
					let (set_id, new_authorities) = new_set.current();

					// we will use the median last finalized number as a hint
					// for the canon block the new authority set should start
					// with. we use the minimum between the median and the local
					// best finalized block.
					let best_finalized_number = self.inner.info().finalized_number;
					let canon_number = best_finalized_number.min(median_last_finalized_number);
					let canon_hash = self.inner.hash(canon_number)
							.map_err(|e| ConsensusError::ClientImport(e.to_string()))?
							.expect(
								"the given block number is less or equal than the current best finalized number; \
								 current best finalized number must exist in chain; qed."
							);

					NewAuthoritySet {
						canon_number,
						canon_hash,
						set_id,
						authorities: new_authorities.to_vec(),
					}
				};
				let old = ::std::mem::replace(guard.as_mut(), new_set);
				guard.set_old(old);

				AppliedChanges::Forced(new_authorities)
			} else {
				let did_standard = guard
					.as_mut()
					.enacts_standard_change(hash, number, &is_descendent_of)
					.map_err(|e| ConsensusError::ClientImport(e.to_string()))
					.map_err(ConsensusError::from)?;

				if let Some(root) = did_standard {
					AppliedChanges::Standard(root)
				} else {
					AppliedChanges::None
				}
			}
		};

		// consume the guard safely and write necessary changes.
		let just_in_case = guard.consume();
		if let Some((_, ref authorities)) = just_in_case {
			let authorities_change = match applied_changes {
				AppliedChanges::Forced(ref new) => Some(new),
				AppliedChanges::Standard(_) => None, // the change isn't actually applied yet.
				AppliedChanges::None => None,
			};

			crate::aux_schema::update_authority_set::<Block, _, _>(
				authorities,
				authorities_change,
				|insert| {
					block
						.auxiliary
						.extend(insert.iter().map(|(k, v)| (k.to_vec(), Some(v.to_vec()))))
				},
			);
		}

		let just_in_case = just_in_case.map(|(o, i)| (o, i.release_mutex()));

		Ok(PendingSetChanges { just_in_case, applied_changes, do_pause })
	}

	/// Read current set id form a given state.
	fn current_set_id(&self, hash: Block::Hash) -> Result<SetId, ConsensusError> {
		let runtime_version = self.inner.runtime_api().version(hash).map_err(|e| {
			ConsensusError::ClientImport(format!(
				"Unable to retrieve current runtime version. {}",
				e
			))
		})?;

		if runtime_version
			.api_version(&<dyn GrandpaApi<Block>>::ID)
			.map_or(false, |v| v < 3)
		{
			// The new API is not supported in this runtime. Try reading directly from storage.
			// This code may be removed once warp sync to an old runtime is no longer needed.
			for prefix in ["GrandpaFinality", "Grandpa"] {
				let k = [twox_128(prefix.as_bytes()), twox_128(b"CurrentSetId")].concat();
				if let Ok(Some(id)) =
					self.inner.storage(hash, &sc_client_api::StorageKey(k.to_vec()))
				{
					if let Ok(id) = SetId::decode(&mut id.0.as_ref()) {
						return Ok(id)
					}
				}
			}
			Err(ConsensusError::ClientImport("Unable to retrieve current set id.".into()))
		} else {
			self.inner
				.runtime_api()
				.current_set_id(hash)
				.map_err(|e| ConsensusError::ClientImport(e.to_string()))
		}
	}

	/// Import whole new state and reset authority set.
	async fn import_state(
		&mut self,
		mut block: BlockImportParams<Block>,
	) -> Result<ImportResult, ConsensusError> {
		let hash = block.post_hash();
		let number = *block.header.number();
		// Force imported state finality.
		block.finalized = true;
		let import_result = (&*self.inner).import_block(block).await;
		match import_result {
			Ok(ImportResult::Imported(aux)) => {
				// We've just imported a new state. We trust the sync module has verified
				// finality proofs and that the state is correct and final.
				// So we can read the authority list and set id from the state.
				self.authority_set_hard_forks.clear();
				let authorities = self
					.inner
					.runtime_api()
					.grandpa_authorities(hash)
					.map_err(|e| ConsensusError::ClientImport(e.to_string()))?;
				let set_id = self.current_set_id(hash)?;
				let authority_set = AuthoritySet::new(
					authorities.clone(),
					set_id,
					fork_tree::ForkTree::new(),
					Vec::new(),
					AuthoritySetChanges::empty(),
				)
				.ok_or_else(|| ConsensusError::ClientImport("Invalid authority list".into()))?;
				*self.authority_set.inner_locked() = authority_set.clone();

				crate::aux_schema::update_authority_set::<Block, _, _>(
					&authority_set,
					None,
					|insert| self.inner.insert_aux(insert, []),
				)
				.map_err(|e| ConsensusError::ClientImport(e.to_string()))?;
				let new_set =
					NewAuthoritySet { canon_number: number, canon_hash: hash, set_id, authorities };
				let _ = self
					.send_voter_commands
					.unbounded_send(VoterCommand::ChangeAuthorities(new_set));
				Ok(ImportResult::Imported(aux))
			},
			Ok(r) => Ok(r),
			Err(e) => Err(ConsensusError::ClientImport(e.to_string())),
		}
	}
}

#[async_trait::async_trait]
impl<BE, Block: BlockT, Client, SC> BlockImport<Block> for GrandpaBlockImport<BE, Block, Client, SC>
where
	NumberFor<Block>: finality_grandpa::BlockNumberOps,
	BE: Backend<Block>,
	Client: ClientForGrandpa<Block, BE>,
	Client::Api: GrandpaApi<Block>,
	for<'a> &'a Client: BlockImport<Block, Error = ConsensusError>,
	SC: Send,
{
	type Error = ConsensusError;

	async fn import_block(
		&mut self,
		mut block: BlockImportParams<Block>,
	) -> Result<ImportResult, Self::Error> {
		let hash = block.post_hash();
		let number = *block.header.number();

		// early exit if block already in chain, otherwise the check for
		// authority changes will error when trying to re-import a change block
		match self.inner.status(hash) {
			Ok(BlockStatus::InChain) => {
				// Strip justifications when re-importing an existing block.
				let _justifications = block.justifications.take();
				return (&*self.inner).import_block(block).await
			},
			Ok(BlockStatus::Unknown) => {},
			Err(e) => return Err(ConsensusError::ClientImport(e.to_string())),
		}

		if block.with_state() {
			return self.import_state(block).await
		}

		if number <= self.inner.info().finalized_number {
			// Importing an old block. Just save justifications and authority set changes
			if self.check_new_change(&block.header, hash).is_some() {
				if block.justifications.is_none() {
					return Err(ConsensusError::ClientImport(
						"Justification required when importing \
							an old block with authority set change."
							.into(),
					))
				}
				assert!(block.justifications.is_some());
				let mut authority_set = self.authority_set.inner_locked();
				authority_set.authority_set_changes.insert(number);
				crate::aux_schema::update_authority_set::<Block, _, _>(
					&authority_set,
					None,
					|insert| {
						block
							.auxiliary
							.extend(insert.iter().map(|(k, v)| (k.to_vec(), Some(v.to_vec()))))
					},
				);
			}
			return (&*self.inner).import_block(block).await
		}

		// on initial sync we will restrict logging under info to avoid spam.
		let initial_sync = block.origin == BlockOrigin::NetworkInitialSync;

		let pending_changes = self.make_authorities_changes(&mut block, hash, initial_sync)?;

		// we don't want to finalize on `inner.import_block`
		let mut justifications = block.justifications.take();
		let import_result = (&*self.inner).import_block(block).await;

		let mut imported_aux = {
			match import_result {
				Ok(ImportResult::Imported(aux)) => aux,
				Ok(r) => {
					debug!(
						target: LOG_TARGET,
						"Restoring old authority set after block import result: {:?}", r,
					);
					pending_changes.revert();
					return Ok(r)
				},
				Err(e) => {
					debug!(
						target: LOG_TARGET,
						"Restoring old authority set after block import error: {}", e,
					);
					pending_changes.revert();
					return Err(ConsensusError::ClientImport(e.to_string()))
				},
			}
		};

		let (applied_changes, do_pause) = pending_changes.defuse();

		// Send the pause signal after import but BEFORE sending a `ChangeAuthorities` message.
		if do_pause {
			let _ = self.send_voter_commands.unbounded_send(VoterCommand::Pause(
				"Forced change scheduled after inactivity".to_string(),
			));
		}

		let needs_justification = applied_changes.needs_justification();

		match applied_changes {
			AppliedChanges::Forced(new) => {
				// NOTE: when we do a force change we are "discrediting" the old set so we
				// ignore any justifications from them. this block may contain a justification
				// which should be checked and imported below against the new authority
				// triggered by this forced change. the new grandpa voter will start at the
				// last median finalized block (which is before the block that enacts the
				// change), full nodes syncing the chain will not be able to successfully
				// import justifications for those blocks since their local authority set view
				// is still of the set before the forced change was enacted, still after #1867
				// they should import the block and discard the justification, and they will
				// then request a justification from sync if it's necessary (which they should
				// then be able to successfully validate).
				let _ =
					self.send_voter_commands.unbounded_send(VoterCommand::ChangeAuthorities(new));

				// we must clear all pending justifications requests, presumably they won't be
				// finalized hence why this forced changes was triggered
				imported_aux.clear_justification_requests = true;
			},
			AppliedChanges::Standard(false) => {
				// we can't apply this change yet since there are other dependent changes that we
				// need to apply first, drop any justification that might have been provided with
				// the block to make sure we request them from `sync` which will ensure they'll be
				// applied in-order.
				justifications.take();
			},
			_ => {},
		}

		let grandpa_justification =
			justifications.and_then(|just| just.into_justification(GRANDPA_ENGINE_ID));

		match grandpa_justification {
			Some(justification) => {
				if environment::should_process_justification(
					&*self.inner,
					self.justification_import_period,
					number,
					needs_justification,
				) {
					let import_res = self.import_justification(
						hash,
						number,
						(GRANDPA_ENGINE_ID, justification),
						needs_justification,
						initial_sync,
					);

					import_res.unwrap_or_else(|err| {
						if needs_justification {
							debug!(
								target: LOG_TARGET,
								"Requesting justification from peers due to imported block #{} that enacts authority set change with invalid justification: {}",
								number,
								err
							);
							imported_aux.bad_justification = true;
							imported_aux.needs_justification = true;
						}
					});
				} else {
					debug!(
						target: LOG_TARGET,
						"Ignoring unnecessary justification for block #{}",
						number,
					);
				}
			},
			None =>
				if needs_justification {
					debug!(
						target: LOG_TARGET,
						"Imported unjustified block #{} that enacts authority set change, waiting for finality for enactment.",
						number,
					);

					imported_aux.needs_justification = true;
				},
		}

		Ok(ImportResult::Imported(imported_aux))
	}

	async fn check_block(
		&mut self,
		block: BlockCheckParams<Block>,
	) -> Result<ImportResult, Self::Error> {
		self.inner.check_block(block).await
	}
}

impl<Backend, Block: BlockT, Client, SC> GrandpaBlockImport<Backend, Block, Client, SC> {
	pub(crate) fn new(
		inner: Arc<Client>,
		justification_import_period: u32,
		select_chain: SC,
		authority_set: SharedAuthoritySet<Block::Hash, NumberFor<Block>>,
		send_voter_commands: TracingUnboundedSender<VoterCommand<Block::Hash, NumberFor<Block>>>,
		authority_set_hard_forks: Vec<(SetId, PendingChange<Block::Hash, NumberFor<Block>>)>,
		justification_sender: GrandpaJustificationSender<Block>,
		telemetry: Option<TelemetryHandle>,
	) -> GrandpaBlockImport<Backend, Block, Client, SC> {
		// check for and apply any forced authority set hard fork that applies
		// to the *current* authority set.
		if let Some((_, change)) = authority_set_hard_forks
			.iter()
			.find(|(set_id, _)| *set_id == authority_set.set_id())
		{
			authority_set.inner().current_authorities = change.next_authorities.clone();
		}

		// index authority set hard forks by block hash so that they can be used
		// by any node syncing the chain and importing a block hard fork
		// authority set changes.
		let authority_set_hard_forks = authority_set_hard_forks
			.into_iter()
			.map(|(_, change)| (change.canon_hash, change))
			.collect::<HashMap<_, _>>();

		// check for and apply any forced authority set hard fork that apply to
		// any *pending* standard changes, checking by the block hash at which
		// they were announced.
		{
			let mut authority_set = authority_set.inner();

			authority_set.pending_standard_changes =
				authority_set.pending_standard_changes.clone().map(&mut |hash, _, original| {
					authority_set_hard_forks.get(hash).cloned().unwrap_or(original)
				});
		}

		GrandpaBlockImport {
			inner,
			justification_import_period,
			select_chain,
			authority_set,
			send_voter_commands,
			authority_set_hard_forks,
			justification_sender,
			telemetry,
			_phantom: PhantomData,
		}
	}
}

impl<BE, Block: BlockT, Client, SC> GrandpaBlockImport<BE, Block, Client, SC>
where
	BE: Backend<Block>,
	Client: ClientForGrandpa<Block, BE>,
	NumberFor<Block>: finality_grandpa::BlockNumberOps,
{
	/// Import a block justification and finalize the block.
	///
	/// If `enacts_change` is set to true, then finalizing this block *must*
	/// enact an authority set change, the function will panic otherwise.
	fn import_justification(
		&mut self,
		hash: Block::Hash,
		number: NumberFor<Block>,
		justification: Justification,
		enacts_change: bool,
		initial_sync: bool,
	) -> Result<(), ConsensusError> {
		if justification.0 != GRANDPA_ENGINE_ID {
			// TODO: the import queue needs to be refactored to be able dispatch to the correct
			// `JustificationImport` instance based on `ConsensusEngineId`, or we need to build a
			// justification import pipeline similar to what we do for `BlockImport`. In the
			// meantime we'll just drop the justification, since this is only used for BEEFY which
			// is still WIP.
			return Ok(())
		}

		let justification = GrandpaJustification::decode_and_verify_finalizes(
			&justification.1,
			(hash, number),
			self.authority_set.set_id(),
			&self.authority_set.current_authorities(),
		);

		let justification = match justification {
			Err(e) => return Err(ConsensusError::ClientImport(e.to_string())),
			Ok(justification) => justification,
		};

		let result = environment::finalize_block(
			self.inner.clone(),
			&self.authority_set,
			None,
			hash,
			number,
			justification.into(),
			initial_sync,
			Some(&self.justification_sender),
			self.telemetry.clone(),
		);

		match result {
			Err(CommandOrError::VoterCommand(command)) => {
				grandpa_log!(
					initial_sync,
					"👴 Imported justification for block #{} that triggers \
					command {}, signaling voter.",
					number,
					command,
				);

				// send the command to the voter
				let _ = self.send_voter_commands.unbounded_send(command);
			},
			Err(CommandOrError::Error(e)) =>
				return Err(match e {
					Error::Grandpa(error) => ConsensusError::ClientImport(error.to_string()),
					Error::Network(error) => ConsensusError::ClientImport(error),
					Error::Blockchain(error) => ConsensusError::ClientImport(error),
					Error::Client(error) => ConsensusError::ClientImport(error.to_string()),
					Error::Safety(error) => ConsensusError::ClientImport(error),
					Error::Signing(error) => ConsensusError::ClientImport(error),
					Error::Timer(error) => ConsensusError::ClientImport(error.to_string()),
					Error::RuntimeApi(error) => ConsensusError::ClientImport(error.to_string()),
				}),
			Ok(_) => {
				assert!(
					!enacts_change,
					"returns Ok when no authority set change should be enacted; qed;"
				);
			},
		}

		Ok(())
	}
}