Storing multiple Justifications per block (#7640)

* primitives/runtime: initial changes on supporting multiple Justifications

* primitives/runtime: make Justifications strongly typed

* Encode/decode Justifications

* primitives/runtime: add Justification type

* backend: apply_finality and finalize_block takes a single Justification

* manual-seal: create engine id and let rpc take encoded justification

* backend: skeleton functions for appending justifications

* backend: initial implementation append_justification

Initial implementation of append_justification on the Backend trait, and also remove unused skeleton
functions for append_justificaton on Finaziler trait.
k

* backend: guard against duplicate consensus engine id

* client/db: add check for block finality

* client/api: add append_justification to in_mem db

* client/light: add no-op append_justification

* network: fix decode call for Justification

* network: only send a single Justification in BlockData

* network: minor comment update

* protocol: update field names to distinguish single justification

* client: further field renames to plural

* client: update function names to plural justifications

* client/db: upgrade existing database for new format

* network: remove dependency on grandpa crate

* db: fix check for finalized block

* grandpa: check for multiple grandpa justifications hwne importing

* backend: update Finalizer trait to take multiple Justifications

* db: remove debugging statements in migration code

* manual-seal: update note about engine id

* db: fix check for finalized block

* client: update variable name to reflect it is now plural

* grandpa: fix incorrect empty Justications in test

* primitives: make Justifications opaque to avoid being empty

* network: fix detecting empty Justification

* runtime: doc strings for Justifications functions

* runtime: add into_justifications

* primitives: check for duplicates in when adding to Justifications

* network/test: use real grandpa engine id in test

* client: fix reviewer comments

* primitives: rename Justifications::push to append

* backend: revert changes to Finalizer trait

* backend: revert mark_finalized

* backend: revert changes to finalize_block

* backend: revert finalized_blocks

* db: add a quick early return for performance

* client: minor reviewer comments

* service/test: use local ConsensusEngineId

* network: add link to issue for sending multiple Justifications

* Apply suggestions from code review

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

* Apply suggestions from code review

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

* network: tweaks to review suggestions

* network: revert change to BlockData for backwards compatibility

* Apply suggestion from code review

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

* Apply suggestions from code review

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* primitives: update doc comment for Justifications

* client/db/upgrade: avoid grandpa crate dependency

* consensus: revert to single Justification for import_justification

* primitives: improve justifications docs

* style cleanups

* use and_then

* client: rename JUSTIFICATIONS db column

* network: revert to using FRNK in network-test

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>
Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>
Co-authored-by: André Silva <andrerfosilva@gmail.com>

substrate/client/api/src/backend.rs

@@ -22,7 +22,7 @@ use std::sync::Arc;
 use std::collections::{HashMap, HashSet};
 use sp_core::ChangesTrieConfigurationRange;
 use sp_core::offchain::OffchainStorage;
-use sp_runtime::{generic::BlockId, Justification, Storage};
+use sp_runtime::{generic::BlockId, Justification, Justifications, Storage};
 use sp_runtime::traits::{Block as BlockT, NumberFor, HashFor};
 use sp_state_machine::{
 	ChangesTrieState, ChangesTrieStorage as StateChangesTrieStorage, ChangesTrieTransaction,
@@ -148,7 +148,7 @@ pub trait BlockImportOperation<Block: BlockT> {
 		&mut self,
 		header: Block::Header,
 		body: Option<Vec<Block::Extrinsic>>,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		state: NewBlockState,
 	) -> sp_blockchain::Result<()>;
 
@@ -197,6 +197,7 @@ pub trait BlockImportOperation<Block: BlockT> {
 		id: BlockId<Block>,
 		justification: Option<Justification>,
 	) -> sp_blockchain::Result<()>;
+
 	/// Mark a block as new head. If both block import and set head are specified, set head
 	/// overrides block import's best block rule.
 	fn mark_head(&mut self, id: BlockId<Block>) -> sp_blockchain::Result<()>;
@@ -230,7 +231,6 @@ pub trait Finalizer<Block: BlockT, B: Backend<Block>> {
 		notify: bool,
 	) -> sp_blockchain::Result<()>;
 
-
 	/// Finalize a block.
 	///
 	/// This will implicitly finalize all blocks up to it and
@@ -250,7 +250,6 @@ pub trait Finalizer<Block: BlockT, B: Backend<Block>> {
 		justification: Option<Justification>,
 		notify: bool,
 	) -> sp_blockchain::Result<()>;
-
 }
 
 /// Provides access to an auxiliary database.
@@ -432,6 +431,15 @@ pub trait Backend<Block: BlockT>: AuxStore + Send + Sync {
 		justification: Option<Justification>,
 	) -> sp_blockchain::Result<()>;
 
+	/// Append justification to the block with the given Id.
+	///
+	/// This should only be called for blocks that are already finalized.
+	fn append_justification(
+		&self,
+		block: BlockId<Block>,
+		justification: Justification,
+	) -> sp_blockchain::Result<()>;
+
 	/// Returns reference to blockchain backend.
 	fn blockchain(&self) -> &Self::Blockchain;
 

substrate/client/api/src/client.rs

@@ -23,7 +23,7 @@ use sp_core::storage::StorageKey;
 use sp_runtime::{
 	traits::{Block as BlockT, NumberFor},
 	generic::{BlockId, SignedBlock},
-	Justification,
+	Justifications,
 };
 use sp_consensus::BlockOrigin;
 
@@ -90,8 +90,8 @@ pub trait BlockBackend<Block: BlockT> {
 	/// Get block status.
 	fn block_status(&self, id: &BlockId<Block>) -> sp_blockchain::Result<sp_consensus::BlockStatus>;
 
-	/// Get block justification set by id.
+	/// Get block justifications for the block with the given id.
-	fn justification(&self, id: &BlockId<Block>) -> sp_blockchain::Result<Option<Justification>>;
+	fn justifications(&self, id: &BlockId<Block>) -> sp_blockchain::Result<Option<Justifications>>;
 
 	/// Get block hash by number.
 	fn block_hash(&self, number: NumberFor<Block>) -> sp_blockchain::Result<Option<Block::Hash>>;

substrate/client/api/src/in_mem.rs

@@ -27,7 +27,7 @@ use sp_core::{
 };
 use sp_runtime::generic::BlockId;
 use sp_runtime::traits::{Block as BlockT, Header as HeaderT, Zero, NumberFor, HashFor};
-use sp_runtime::{Justification, Storage};
+use sp_runtime::{Justification, Justifications, Storage};
 use sp_state_machine::{
 	ChangesTrieTransaction, InMemoryBackend, Backend as StateBackend, StorageCollection,
 	ChildStorageCollection,
@@ -51,12 +51,12 @@ struct PendingBlock<B: BlockT> {
 
 #[derive(PartialEq, Eq, Clone)]
 enum StoredBlock<B: BlockT> {
-	Header(B::Header, Option<Justification>),
+	Header(B::Header, Option<Justifications>),
-	Full(B, Option<Justification>),
+	Full(B, Option<Justifications>),
 }
 
 impl<B: BlockT> StoredBlock<B> {
-	fn new(header: B::Header, body: Option<Vec<B::Extrinsic>>, just: Option<Justification>) -> Self {
+	fn new(header: B::Header, body: Option<Vec<B::Extrinsic>>, just: Option<Justifications>) -> Self {
 		match body {
 			Some(body) => StoredBlock::Full(B::new(header, body), just),
 			None => StoredBlock::Header(header, just),
@@ -70,7 +70,7 @@ impl<B: BlockT> StoredBlock<B> {
 		}
 	}
 
-	fn justification(&self) -> Option<&Justification> {
+	fn justifications(&self) -> Option<&Justifications> {
 		match *self {
 			StoredBlock::Header(_, ref j) | StoredBlock::Full(_, ref j) => j.as_ref()
 		}
@@ -83,7 +83,7 @@ impl<B: BlockT> StoredBlock<B> {
 		}
 	}
 
-	fn into_inner(self) -> (B::Header, Option<Vec<B::Extrinsic>>, Option<Justification>) {
+	fn into_inner(self) -> (B::Header, Option<Vec<B::Extrinsic>>, Option<Justifications>) {
 		match self {
 			StoredBlock::Header(header, just) => (header, None, just),
 			StoredBlock::Full(block, just) => {
@@ -164,7 +164,7 @@ impl<Block: BlockT> Blockchain<Block> {
 		&self,
 		hash: Block::Hash,
 		header: <Block as BlockT>::Header,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		body: Option<Vec<<Block as BlockT>::Extrinsic>>,
 		new_state: NewBlockState,
 	) -> sp_blockchain::Result<()> {
@@ -176,7 +176,7 @@ impl<Block: BlockT> Blockchain<Block> {
 		{
 			let mut storage = self.storage.write();
 			storage.leaves.import(hash.clone(), number.clone(), header.parent_hash().clone());
-			storage.blocks.insert(hash.clone(), StoredBlock::new(header, body, justification));
+			storage.blocks.insert(hash.clone(), StoredBlock::new(header, body, justifications));
 
 			if let NewBlockState::Final = new_state {
 				storage.finalized_hash = hash;
@@ -285,16 +285,44 @@ impl<Block: BlockT> Blockchain<Block> {
 			let block = storage.blocks.get_mut(&hash)
 				.expect("hash was fetched from a block in the db; qed");
 
-			let block_justification = match block {
+			let block_justifications = match block {
 				StoredBlock::Header(_, ref mut j) | StoredBlock::Full(_, ref mut j) => j
 			};
 
-			*block_justification = justification;
+			*block_justifications = justification.map(Justifications::from);
 		}
 
 		Ok(())
 	}
 
+	fn append_justification(&self, id: BlockId<Block>, justification: Justification)
+		-> sp_blockchain::Result<()>
+	{
+		let hash = self.expect_block_hash_from_id(&id)?;
+		let mut storage = self.storage.write();
+
+		let block = storage
+			.blocks
+			.get_mut(&hash)
+			.expect("hash was fetched from a block in the db; qed");
+
+		let block_justifications = match block {
+			StoredBlock::Header(_, ref mut j) | StoredBlock::Full(_, ref mut j) => j
+		};
+
+		if let Some(stored_justifications) = block_justifications {
+			if !stored_justifications.append(justification) {
+				return Err(sp_blockchain::Error::BadJustification(
+					"Duplicate consensus engine ID".into()
+				));
+			}
+		} else {
+			*block_justifications = Some(Justifications::from(justification));
+		};
+
+		Ok(())
+	}
+
 	fn write_aux(&self, ops: Vec<(Vec<u8>, Option<Vec<u8>>)>) {
 		let mut storage = self.storage.write();
 		for (k, v) in ops {
@@ -365,9 +393,9 @@ impl<Block: BlockT> blockchain::Backend<Block> for Blockchain<Block> {
 		}))
 	}
 
-	fn justification(&self, id: BlockId<Block>) -> sp_blockchain::Result<Option<Justification>> {
+	fn justifications(&self, id: BlockId<Block>) -> sp_blockchain::Result<Option<Justifications>> {
 		Ok(self.id(id).and_then(|hash| self.storage.read().blocks.get(&hash).and_then(|b|
-			b.justification().map(|x| x.clone()))
+			b.justifications().map(|x| x.clone()))
 		))
 	}
 
@@ -508,12 +536,12 @@ impl<Block: BlockT> backend::BlockImportOperation<Block> for BlockImportOperatio
 		&mut self,
 		header: <Block as BlockT>::Header,
 		body: Option<Vec<<Block as BlockT>::Extrinsic>>,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		state: NewBlockState,
 	) -> sp_blockchain::Result<()> {
 		assert!(self.pending_block.is_none(), "Only one block per operation is allowed");
 		self.pending_block = Some(PendingBlock {
-			block: StoredBlock::new(header, body, justification),
+			block: StoredBlock::new(header, body, justifications),
 			state,
 		});
 		Ok(())
@@ -696,6 +724,14 @@ impl<Block: BlockT> backend::Backend<Block> for Backend<Block> where Block::Hash
 		self.blockchain.finalize_header(block, justification)
 	}
 
+	fn append_justification(
+		&self,
+		block: BlockId<Block>,
+		justification: Justification,
+	) -> sp_blockchain::Result<()> {
+		self.blockchain.append_justification(block, justification)
+	}
+
 	fn blockchain(&self) -> &Self::Blockchain {
 		&self.blockchain
 	}
@@ -766,3 +802,64 @@ pub fn check_genesis_storage(storage: &Storage) -> sp_blockchain::Result<()> {
 
 	Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+	use crate::{NewBlockState, in_mem::Blockchain};
+	use sp_api::{BlockId, HeaderT};
+	use sp_runtime::{ConsensusEngineId, Justifications};
+	use sp_blockchain::Backend;
+	use substrate_test_runtime::{Block, Header, H256};
+
+	pub const ID1: ConsensusEngineId = *b"TST1";
+	pub const ID2: ConsensusEngineId = *b"TST2";
+
+	fn header(number: u64) -> Header {
+		let parent_hash = match number {
+			0 => Default::default(),
+			_ => header(number - 1).hash(),
+		};
+		Header::new(number, H256::from_low_u64_be(0), H256::from_low_u64_be(0), parent_hash, Default::default())
+	}
+
+	fn test_blockchain() -> Blockchain<Block> {
+		let blockchain = Blockchain::<Block>::new();
+		let just0 = Some(Justifications::from((ID1, vec![0])));
+		let just1 = Some(Justifications::from((ID1, vec![1])));
+		let just2 = None;
+		let just3 = Some(Justifications::from((ID1, vec![3])));
+		blockchain.insert(header(0).hash(), header(0), just0, None, NewBlockState::Final).unwrap();
+		blockchain.insert(header(1).hash(), header(1), just1, None, NewBlockState::Final).unwrap();
+		blockchain.insert(header(2).hash(), header(2), just2, None, NewBlockState::Best).unwrap();
+		blockchain.insert(header(3).hash(), header(3), just3, None, NewBlockState::Final).unwrap();
+		blockchain
+	}
+
+	#[test]
+	fn append_and_retrieve_justifications() {
+		let blockchain = test_blockchain();
+		let last_finalized = blockchain.last_finalized().unwrap();
+		let block = BlockId::Hash(last_finalized);
+
+		blockchain.append_justification(block, (ID2, vec![4])).unwrap();
+		let justifications = {
+			let mut just = Justifications::from((ID1, vec![3]));
+			just.append((ID2, vec![4]));
+			just
+		};
+		assert_eq!(blockchain.justifications(block).unwrap(), Some(justifications));
+	}
+
+	#[test]
+	fn store_duplicate_justifications_is_forbidden() {
+		let blockchain = test_blockchain();
+		let last_finalized = blockchain.last_finalized().unwrap();
+		let block = BlockId::Hash(last_finalized);
+
+		blockchain.append_justification(block, (ID2, vec![0])).unwrap();
+		assert!(matches!(
+			blockchain.append_justification(block, (ID2, vec![1])),
+			Err(sp_blockchain::Error::BadJustification(_)),
+		));
+	}
+}

substrate/client/consensus/aura/src/import_queue.rs

@@ -39,7 +39,7 @@ use sp_consensus::{
 use sc_client_api::{backend::AuxStore, BlockOf};
 use sp_blockchain::{well_known_cache_keys::{self, Id as CacheKeyId}, ProvideCache, HeaderBackend};
 use sp_block_builder::BlockBuilder as BlockBuilderApi;
-use sp_runtime::{generic::{BlockId, OpaqueDigestItemId}, Justification};
+use sp_runtime::{generic::{BlockId, OpaqueDigestItemId}, Justifications};
 use sp_runtime::traits::{Block as BlockT, Header, DigestItemFor, Zero};
 use sp_api::ProvideRuntimeApi;
 use sp_core::crypto::Pair;
@@ -238,7 +238,7 @@ impl<B: BlockT, C, P, CAW> Verifier<B> for AuraVerifier<C, P, CAW> where
 		&mut self,
 		origin: BlockOrigin,
 		header: B::Header,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		mut body: Option<Vec<B::Extrinsic>>,
 	) -> Result<(BlockImportParams<B, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String> {
 		let mut inherent_data = self.inherent_data_providers
@@ -317,7 +317,7 @@ impl<B: BlockT, C, P, CAW> Verifier<B> for AuraVerifier<C, P, CAW> where
 				let mut import_block = BlockImportParams::new(origin, pre_header);
 				import_block.post_digests.push(seal);
 				import_block.body = body;
-				import_block.justification = justification;
+				import_block.justifications = justifications;
 				import_block.fork_choice = Some(ForkChoiceStrategy::LongestChain);
 				import_block.post_hash = Some(hash);
 

substrate/client/consensus/babe/src/lib.rs

@@ -84,7 +84,7 @@ use sp_core::crypto::Public;
 use sp_application_crypto::AppKey;
 use sp_keystore::{SyncCryptoStorePtr, SyncCryptoStore};
 use sp_runtime::{
-	generic::{BlockId, OpaqueDigestItemId}, Justification,
+	generic::{BlockId, OpaqueDigestItemId}, Justifications,
 	traits::{Block as BlockT, Header, DigestItemFor, Zero},
 };
 use sp_api::{ProvideRuntimeApi, NumberFor};
@@ -1097,15 +1097,15 @@ where
 		&mut self,
 		origin: BlockOrigin,
 		header: Block::Header,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		mut body: Option<Vec<Block::Extrinsic>>,
 	) -> Result<(BlockImportParams<Block, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String> {
 		trace!(
 			target: "babe",
-			"Verifying origin: {:?} header: {:?} justification: {:?} body: {:?}",
+			"Verifying origin: {:?} header: {:?} justification(s): {:?} body: {:?}",
 			origin,
 			header,
-			justification,
+			justifications,
 			body,
 		);
 
@@ -1194,7 +1194,7 @@ where
 				let mut import_block = BlockImportParams::new(origin, pre_header);
 				import_block.post_digests.push(verified_info.seal);
 				import_block.body = body;
-				import_block.justification = justification;
+				import_block.justifications = justifications;
 				import_block.intermediates.insert(
 					Cow::from(INTERMEDIATE_KEY),
 					Box::new(BabeIntermediate::<Block> { epoch_descriptor }) as Box<dyn Any>,

substrate/client/consensus/babe/src/tests.rs

@@ -235,12 +235,12 @@ impl Verifier<TestBlock> for TestVerifier {
 		&mut self,
 		origin: BlockOrigin,
 		mut header: TestHeader,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		body: Option<Vec<TestExtrinsic>>,
 	) -> Result<(BlockImportParams<TestBlock, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String> {
 		// apply post-sealing mutations (i.e. stripping seal, if desired).
 		(self.mutator)(&mut header, Stage::PostSeal);
-		self.inner.verify(origin, header, justification, body)
+		self.inner.verify(origin, header, justifications, body)
 	}
 }
 

substrate/client/consensus/manual-seal/src/lib.rs

@@ -27,7 +27,7 @@ use sp_consensus::{
 };
 use sp_blockchain::HeaderBackend;
 use sp_inherents::InherentDataProviders;
-use sp_runtime::{traits::Block as BlockT, Justification};
+use sp_runtime::{traits::Block as BlockT, Justifications, ConsensusEngineId};
 use sc_client_api::backend::{Backend as ClientBackend, Finalizer};
 use sc_transaction_pool::txpool;
 use std::{sync::Arc, marker::PhantomData};
@@ -49,6 +49,9 @@ pub use self::{
 };
 use sp_api::{ProvideRuntimeApi, TransactionFor};
 
+/// The `ConsensusEngineId` of Manual Seal.
+pub const MANUAL_SEAL_ENGINE_ID: ConsensusEngineId = [b'm', b'a', b'n', b'l'];
+
 /// The verifier for the manual seal engine; instantly finalizes.
 struct ManualSealVerifier;
 
@@ -57,11 +60,11 @@ impl<B: BlockT> Verifier<B> for ManualSealVerifier {
 		&mut self,
 		origin: BlockOrigin,
 		header: B::Header,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		body: Option<Vec<B::Extrinsic>>,
 	) -> Result<(BlockImportParams<B, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String> {
 		let mut import_params = BlockImportParams::new(origin, header);
-		import_params.justification = justification;
+		import_params.justifications = justifications;
 		import_params.body = body;
 		import_params.finalized = false;
 		import_params.fork_choice = Some(ForkChoiceStrategy::LongestChain);
@@ -193,6 +196,7 @@ pub async fn run_manual_seal<B, BI, CB, E, C, A, SC, CS>(
 				).await;
 			}
 			EngineCommand::FinalizeBlock { hash, sender, justification } => {
+				let justification = justification.map(|j| (MANUAL_SEAL_ENGINE_ID, j));
 				finalize_block(
 					FinalizeBlockParams {
 						hash,

substrate/client/consensus/manual-seal/src/rpc.rs

@@ -28,7 +28,7 @@ use futures::{
 	SinkExt
 };
 use serde::{Deserialize, Serialize};
-use sp_runtime::Justification;
+use sp_runtime::EncodedJustification;
 pub use self::gen_client::Client as ManualSealClient;
 
 /// Future's type for jsonrpc
@@ -62,7 +62,7 @@ pub enum EngineCommand<Hash> {
 		/// sender to report errors/success to the rpc.
 		sender: Sender<()>,
 		/// finalization justification
-		justification: Option<Justification>,
+		justification: Option<EncodedJustification>,
 	}
 }
 
@@ -83,7 +83,7 @@ pub trait ManualSealApi<Hash> {
 	fn finalize_block(
 		&self,
 		hash: Hash,
-		justification: Option<Justification>
+		justification: Option<EncodedJustification>
 	) -> FutureResult<bool>;
 }
 
@@ -131,7 +131,7 @@ impl<Hash: Send + 'static> ManualSealApi<Hash> for ManualSeal<Hash> {
 		Box::new(future.map_err(Error::from).compat())
 	}
 
-	fn finalize_block(&self, hash: Hash, justification: Option<Justification>) -> FutureResult<bool> {
+	fn finalize_block(&self, hash: Hash, justification: Option<EncodedJustification>) -> FutureResult<bool> {
 		let mut sink = self.import_block_channel.clone();
 		let future = async move {
 			let (sender, receiver) = oneshot::channel();

substrate/client/consensus/pow/src/lib.rs

@@ -44,7 +44,7 @@ use parking_lot::Mutex;
 use sc_client_api::{BlockOf, backend::AuxStore, BlockchainEvents};
 use sp_blockchain::{HeaderBackend, ProvideCache, well_known_cache_keys::Id as CacheKeyId};
 use sp_block_builder::BlockBuilder as BlockBuilderApi;
-use sp_runtime::{Justification, RuntimeString};
+use sp_runtime::{Justifications, RuntimeString};
 use sp_runtime::generic::{BlockId, Digest, DigestItem};
 use sp_runtime::traits::{Block as BlockT, Header as HeaderT};
 use sp_api::ProvideRuntimeApi;
@@ -457,7 +457,7 @@ impl<B: BlockT, Algorithm> Verifier<B> for PowVerifier<B, Algorithm> where
 		&mut self,
 		origin: BlockOrigin,
 		header: B::Header,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		body: Option<Vec<B::Extrinsic>>,
 	) -> Result<(BlockImportParams<B, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String> {
 		let hash = header.hash();
@@ -470,7 +470,7 @@ impl<B: BlockT, Algorithm> Verifier<B> for PowVerifier<B, Algorithm> where
 		let mut import_block = BlockImportParams::new(origin, checked_header);
 		import_block.post_digests.push(seal);
 		import_block.body = body;
-		import_block.justification = justification;
+		import_block.justifications = justifications;
 		import_block.intermediates.insert(
 			Cow::from(INTERMEDIATE_KEY),
 			Box::new(intermediate) as Box<dyn Any>

substrate/client/db/src/changes_tries_storage.rs

@@ -955,7 +955,8 @@ mod tests {
 		let block0 = insert_header_with_configuration_change(&backend, 0, Default::default(), None, config0);
 		let config1 = Some(ChangesTrieConfiguration::new(2, 6));
 		let block1 = insert_header_with_configuration_change(&backend, 1, block0, changes(0), config1);
-		backend.finalize_block(BlockId::Number(1), Some(vec![42])).unwrap();
+		let just1 = Some((*b"TEST", vec![42]));
+		backend.finalize_block(BlockId::Number(1), just1).unwrap();
 		let config2 = Some(ChangesTrieConfiguration::new(2, 7));
 		let block2 = insert_header_with_configuration_change(&backend, 2, block1, changes(1), config2);
 		let config2_1 = Some(ChangesTrieConfiguration::new(2, 8));

substrate/client/db/src/lib.rs

@@ -57,10 +57,11 @@ use sc_client_api::{
 	UsageInfo, MemoryInfo, IoInfo, MemorySize,
 	backend::{NewBlockState, PrunableStateChangesTrieStorage, ProvideChtRoots},
 	leaves::{LeafSet, FinalizationDisplaced}, cht,
+	utils::is_descendent_of,
 };
 use sp_blockchain::{
 	Result as ClientResult, Error as ClientError,
-	well_known_cache_keys, HeaderBackend,
+	well_known_cache_keys, Backend as _, HeaderBackend,
 };
 use codec::{Decode, Encode};
 use hash_db::Prefix;
@@ -70,7 +71,7 @@ use sp_core::{Hasher, ChangesTrieConfiguration};
 use sp_core::offchain::OffchainOverlayedChange;
 use sp_core::storage::{well_known_keys, ChildInfo};
 use sp_arithmetic::traits::Saturating;
-use sp_runtime::{generic::{DigestItem, BlockId}, Justification, Storage};
+use sp_runtime::{generic::{DigestItem, BlockId}, Justification, Justifications, Storage};
 use sp_runtime::traits::{
 	Block as BlockT, Header as HeaderT, NumberFor, Zero, One, SaturatedConversion, HashFor,
 };
@@ -351,7 +352,7 @@ pub(crate) mod columns {
 	pub const KEY_LOOKUP: u32 = 3;
 	pub const HEADER: u32 = 4;
 	pub const BODY: u32 = 5;
-	pub const JUSTIFICATION: u32 = 6;
+	pub const JUSTIFICATIONS: u32 = 6;
 	pub const CHANGES_TRIE: u32 = 7;
 	pub const AUX: u32 = 8;
 	/// Offchain workers local storage
@@ -363,7 +364,7 @@ pub(crate) mod columns {
 
 struct PendingBlock<Block: BlockT> {
 	header: Block::Header,
-	justification: Option<Justification>,
+	justifications: Option<Justifications>,
 	body: Option<Vec<Block::Extrinsic>>,
 	leaf_state: NewBlockState,
 }
@@ -535,8 +536,8 @@ impl<Block: BlockT> sc_client_api::blockchain::Backend<Block> for BlockchainDb<B
 		}
 	}
 
-	fn justification(&self, id: BlockId<Block>) -> ClientResult<Option<Justification>> {
+	fn justifications(&self, id: BlockId<Block>) -> ClientResult<Option<Justifications>> {
-		match read_db(&*self.db, columns::KEY_LOOKUP, columns::JUSTIFICATION, id)? {
+		match read_db(&*self.db, columns::KEY_LOOKUP, columns::JUSTIFICATIONS, id)? {
 			Some(justification) => match Decode::decode(&mut &justification[..]) {
 				Ok(justification) => Ok(Some(justification)),
 				Err(err) => return Err(sp_blockchain::Error::Backend(
@@ -716,7 +717,7 @@ impl<Block: BlockT> sc_client_api::backend::BlockImportOperation<Block> for Bloc
 		&mut self,
 		header: Block::Header,
 		body: Option<Vec<Block::Extrinsic>>,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		leaf_state: NewBlockState,
 	) -> ClientResult<()> {
 		assert!(self.pending_block.is_none(), "Only one block per operation is allowed");
@@ -726,7 +727,7 @@ impl<Block: BlockT> sc_client_api::backend::BlockImportOperation<Block> for Bloc
 		self.pending_block = Some(PendingBlock {
 			header,
 			body,
-			justification,
+			justifications,
 			leaf_state,
 		});
 		Ok(())
@@ -1130,9 +1131,9 @@ impl<Block: BlockT> Backend<Block> {
 
 		if let Some(justification) = justification {
 			transaction.set_from_vec(
-				columns::JUSTIFICATION,
+				columns::JUSTIFICATIONS,
 				&utils::number_and_hash_to_lookup_key(number, hash)?,
-				justification.encode(),
+				Justifications::from(justification).encode(),
 			);
 		}
 		Ok((*hash, number, false, true))
@@ -1241,8 +1242,8 @@ impl<Block: BlockT> Backend<Block> {
 					},
 				}
 			}
-			if let Some(justification) = pending_block.justification {
+			if let Some(justifications) = pending_block.justifications {
-				transaction.set_from_vec(columns::JUSTIFICATION, &lookup_key, justification.encode());
+				transaction.set_from_vec(columns::JUSTIFICATIONS, &lookup_key, justifications.encode());
 			}
 
 			if number.is_zero() {
@@ -1409,7 +1410,7 @@ impl<Block: BlockT> Backend<Block> {
 
 		self.storage.db.commit(transaction)?;
 
-		// Apply all in-memory state shanges.
+		// Apply all in-memory state changes.
 		// Code beyond this point can't fail.
 
 		if let Some((
@@ -1668,6 +1669,50 @@ impl<Block: BlockT> sc_client_api::backend::Backend<Block> for Backend<Block> {
 		Ok(())
 	}
 
+	fn append_justification(
+		&self,
+		block: BlockId<Block>,
+		justification: Justification,
+	) -> ClientResult<()> {
+		let mut transaction: Transaction<DbHash> = Transaction::new();
+		let hash = self.blockchain.expect_block_hash_from_id(&block)?;
+		let header = self.blockchain.expect_header(block)?;
+		let number = *header.number();
+
+		// Check if the block is finalized first.
+		let is_descendent_of = is_descendent_of(&self.blockchain, None);
+		let last_finalized = self.blockchain.last_finalized()?;
+
+		// We can do a quick check first, before doing a proper but more expensive check
+		if number > self.blockchain.info().finalized_number
+			|| (hash != last_finalized && !is_descendent_of(&hash, &last_finalized)?)
+		{
+			return Err(ClientError::NotInFinalizedChain);
+		}
+
+		let justifications =
+			if let Some(mut stored_justifications) = self.blockchain.justifications(block)? {
+				if !stored_justifications.append(justification) {
+					return Err(ClientError::BadJustification(
+						"Duplicate consensus engine ID".into()
+					));
+				}
+				stored_justifications
+			} else {
+				Justifications::from(justification)
+			};
+
+		transaction.set_from_vec(
+			columns::JUSTIFICATIONS,
+			&utils::number_and_hash_to_lookup_key(number, hash)?,
+			justifications.encode(),
+		);
+
+		self.storage.db.commit(transaction)?;
+
+		Ok(())
+	}
+
 	fn changes_trie_storage(&self) -> Option<&dyn PrunableStateChangesTrieStorage<Block>> {
 		Some(&self.changes_tries_storage)
 	}
@@ -1918,12 +1963,16 @@ pub(crate) mod tests {
 	use sp_core::H256;
 	use sc_client_api::backend::{Backend as BTrait, BlockImportOperation as Op};
 	use sc_client_api::blockchain::Backend as BLBTrait;
+	use sp_runtime::ConsensusEngineId;
 	use sp_runtime::testing::{Header, Block as RawBlock, ExtrinsicWrapper};
 	use sp_runtime::traits::{Hash, BlakeTwo256};
 	use sp_runtime::generic::DigestItem;
 	use sp_state_machine::{TrieMut, TrieDBMut};
 	use sp_blockchain::{lowest_common_ancestor, tree_route};
 
+	const CONS0_ENGINE_ID: ConsensusEngineId = *b"CON0";
+	const CONS1_ENGINE_ID: ConsensusEngineId = *b"CON1";
+
 	pub(crate) type Block = RawBlock<ExtrinsicWrapper<u64>>;
 
 	pub fn prepare_changes(changes: Vec<(Vec<u8>, Vec<u8>)>) -> (H256, MemoryDB<BlakeTwo256>) {
@@ -2511,12 +2560,47 @@ pub(crate) mod tests {
 		let block0 = insert_header(&backend, 0, Default::default(), None, Default::default());
 		let _ = insert_header(&backend, 1, block0, None, Default::default());
 
-		let justification = Some(vec![1, 2, 3]);
+		let justification = Some((CONS0_ENGINE_ID, vec![1, 2, 3]));
 		backend.finalize_block(BlockId::Number(1), justification.clone()).unwrap();
 
 		assert_eq!(
-			backend.blockchain().justification(BlockId::Number(1)).unwrap(),
+			backend.blockchain().justifications(BlockId::Number(1)).unwrap(),
-			justification,
+			justification.map(Justifications::from),
+		);
+	}
+
+	#[test]
+	fn test_append_justification_to_finalized_block() {
+		use sc_client_api::blockchain::{Backend as BlockChainBackend};
+
+		let backend = Backend::<Block>::new_test(10, 10);
+
+		let block0 = insert_header(&backend, 0, Default::default(), None, Default::default());
+		let _ = insert_header(&backend, 1, block0, None, Default::default());
+
+		let just0 = (CONS0_ENGINE_ID, vec![1, 2, 3]);
+		backend.finalize_block(
+			BlockId::Number(1),
+			Some(just0.clone().into()),
+		).unwrap();
+
+		let just1 = (CONS1_ENGINE_ID, vec![4, 5]);
+		backend.append_justification(BlockId::Number(1), just1.clone()).unwrap();
+
+		let just2 = (CONS1_ENGINE_ID, vec![6, 7]);
+		assert!(matches!(
+			backend.append_justification(BlockId::Number(1), just2),
+			Err(ClientError::BadJustification(_))
+		));
+
+		let justifications = {
+			let mut just = Justifications::from(just0);
+			just.append(just1);
+			just
+		};
+		assert_eq!(
+			backend.blockchain().justifications(BlockId::Number(1)).unwrap(),
+			Some(justifications),
 		);
 	}
 

substrate/client/db/src/upgrade.rs

@@ -23,17 +23,19 @@ use std::io::{Read, Write, ErrorKind};
 use std::path::{Path, PathBuf};
 
 use sp_runtime::traits::Block as BlockT;
-use crate::utils::DatabaseType;
+use crate::{columns, utils::DatabaseType};
 use kvdb_rocksdb::{Database, DatabaseConfig};
+use codec::Encode;
 
 /// Version file name.
 const VERSION_FILE_NAME: &'static str = "db_version";
 
 /// Current db version.
-const CURRENT_VERSION: u32 = 2;
+const CURRENT_VERSION: u32 = 3;
 
 /// Number of columns in v1.
 const V1_NUM_COLUMNS: u32 = 11;
+const V2_NUM_COLUMNS: u32 = 12;
 
 /// Upgrade database to current version.
 pub fn upgrade_db<Block: BlockT>(db_path: &Path, db_type: DatabaseType) -> sp_blockchain::Result<()> {
@@ -42,7 +44,11 @@ pub fn upgrade_db<Block: BlockT>(db_path: &Path, db_type: DatabaseType) -> sp_bl
 		let db_version = current_version(db_path)?;
 		match db_version {
 			0 => Err(sp_blockchain::Error::Backend(format!("Unsupported database version: {}", db_version)))?,
-			1 => migrate_1_to_2::<Block>(db_path, db_type)?,
+			1 => {
+				migrate_1_to_2::<Block>(db_path, db_type)?;
+				migrate_2_to_3::<Block>(db_path, db_type)?
+			},
+			2 => migrate_2_to_3::<Block>(db_path, db_type)?,
 			CURRENT_VERSION => (),
 			_ => Err(sp_blockchain::Error::Backend(format!("Future database version: {}", db_version)))?,
 		}
@@ -62,6 +68,31 @@ fn migrate_1_to_2<Block: BlockT>(db_path: &Path, _db_type: DatabaseType) -> sp_b
 	db.add_column().map_err(db_err)
 }
 
+/// Migration from version2 to version3:
+/// - The format of the stored Justification changed to support multiple Justifications.
+fn migrate_2_to_3<Block: BlockT>(db_path: &Path, _db_type: DatabaseType) -> sp_blockchain::Result<()> {
+	let db_path = db_path.to_str()
+		.ok_or_else(|| sp_blockchain::Error::Backend("Invalid database path".into()))?;
+	let db_cfg = DatabaseConfig::with_columns(V2_NUM_COLUMNS);
+	let db = Database::open(&db_cfg, db_path).map_err(db_err)?;
+
+	// Get all the keys we need to update
+	let keys: Vec<_> = db.iter(columns::JUSTIFICATIONS).map(|entry| entry.0).collect();
+
+	// Read and update each entry
+	let mut transaction = db.transaction();
+	for key in keys {
+		if let Some(justification) = db.get(columns::JUSTIFICATIONS, &key).map_err(db_err)? {
+			// Tag each Justification with the hardcoded ID for GRANDPA. Avoid the dependency on the GRANDPA crate
+			let justifications = sp_runtime::Justifications::from((*b"FRNK", justification));
+			transaction.put_vec(columns::JUSTIFICATIONS, &key, justifications.encode());
+		}
+	}
+	db.write(transaction).map_err(db_err)?;
+
+	Ok(())
+}
+
 /// Reads current database version from the file at given path.
 /// If the file does not exist returns 0.
 fn current_version(path: &Path) -> sp_blockchain::Result<u32> {
@@ -141,8 +172,8 @@ mod tests {
 	}
 
 	#[test]
-	fn upgrade_from_1_to_2_works() {
+	fn upgrade_to_3_works() {
-		for version_from_file in &[None, Some(1)] {
+		for version_from_file in &[None, Some(1), Some(2)] {
 			let db_dir = tempfile::TempDir::new().unwrap();
 			let db_path = db_dir.path();
 			create_db(db_path, *version_from_file);

substrate/client/finality-grandpa-warp-sync/src/proof.rs

@@ -20,7 +20,7 @@ use sc_finality_grandpa::{
 	find_scheduled_change, AuthoritySetChanges, BlockNumberOps, GrandpaJustification,
 };
 use sp_blockchain::Backend as BlockchainBackend;
-use sp_finality_grandpa::{AuthorityList, SetId};
+use sp_finality_grandpa::{AuthorityList, SetId, GRANDPA_ENGINE_ID};
 use sp_runtime::{
 	generic::BlockId,
 	traits::{Block as BlockT, NumberFor},
@@ -108,11 +108,14 @@ impl<Block: BlockT> WarpSyncProof<Block> {
 				break;
 			}
 
-			let justification = backend.justification(BlockId::Number(*last_block))?.expect(
+			let justification = backend
-				"header is last in set and contains standard change signal; \
+				.justifications(BlockId::Number(*last_block))?
-				 must have justification; \
+				.and_then(|just| just.into_justification(GRANDPA_ENGINE_ID))
-				 qed.",
+				.expect(
-			);
+					"header is last in set and contains standard change signal; \
+					must have justification; \
+					qed.",
+				);
 
 			let justification = GrandpaJustification::<Block>::decode(&mut &justification[..])?;
 
@@ -171,6 +174,7 @@ mod tests {
 	use sc_finality_grandpa::{AuthoritySetChanges, GrandpaJustification};
 	use sp_blockchain::HeaderBackend;
 	use sp_consensus::BlockOrigin;
+	use sp_finality_grandpa::GRANDPA_ENGINE_ID;
 	use sp_keyring::Ed25519Keyring;
 	use sp_runtime::{generic::BlockId, traits::Header as _};
 	use std::sync::Arc;
@@ -272,7 +276,10 @@ mod tests {
 				let justification = GrandpaJustification::from_commit(&client, 42, commit).unwrap();
 
 				client
-					.finalize_block(BlockId::Hash(target_hash), Some(justification.encode()))
+					.finalize_block(
+						BlockId::Hash(target_hash),
+						Some((GRANDPA_ENGINE_ID, justification.encode()))
+					)
 					.unwrap();
 
 				authority_set_changes.push((current_set_id, n));

substrate/client/finality-grandpa/src/environment.rs

@@ -55,7 +55,7 @@ use crate::justification::GrandpaJustification;
 use crate::until_imported::UntilVoteTargetImported;
 use crate::voting_rule::VotingRule;
 use sp_finality_grandpa::{
-	AuthorityId, AuthoritySignature, Equivocation, EquivocationProof,
+	AuthorityId, AuthoritySignature, Equivocation, EquivocationProof, GRANDPA_ENGINE_ID,
 	GrandpaApi, RoundNumber, SetId,
 };
 use prometheus_endpoint::{register, Counter, Gauge, PrometheusError, U64};
@@ -1326,10 +1326,13 @@ where
 
 		// ideally some handle to a synchronization oracle would be used
 		// to avoid unconditionally notifying.
-		client.apply_finality(import_op, BlockId::Hash(hash), justification, true).map_err(|e| {
+		let justification = justification.map(|j| (GRANDPA_ENGINE_ID, j.clone()));
-			warn!(target: "afg", "Error applying finality to block {:?}: {:?}", (hash, number), e);
+		client
-			e
+			.apply_finality(import_op, BlockId::Hash(hash), justification, true)
-		})?;
+			.map_err(|e| {
+				warn!(target: "afg", "Error applying finality to block {:?}: {:?}", (hash, number), e);
+				e
+			})?;
 		telemetry!(
 			telemetry;
 			CONSENSUS_INFO;

substrate/client/finality-grandpa/src/finality_proof.rs

@@ -43,11 +43,11 @@ use finality_grandpa::BlockNumberOps;
 use parity_scale_codec::{Encode, Decode};
 use sp_blockchain::{Backend as BlockchainBackend, Error as ClientError, Result as ClientResult};
 use sp_runtime::{
-	Justification, generic::BlockId,
+	EncodedJustification, generic::BlockId,
 	traits::{NumberFor, Block as BlockT, Header as HeaderT, One},
 };
 use sc_client_api::backend::Backend;
-use sp_finality_grandpa::AuthorityId;
+use sp_finality_grandpa::{AuthorityId, GRANDPA_ENGINE_ID};
 
 use crate::authorities::AuthoritySetChanges;
 use crate::justification::GrandpaJustification;
@@ -190,8 +190,10 @@ where
 	// Get the Justification stored at the last block of the set
 	let last_block_for_set_id = BlockId::Number(last_block_for_set);
 	let justification =
-		if let Some(justification) = blockchain.justification(last_block_for_set_id)? {
+		if let Some(grandpa_justification) = blockchain.justifications(last_block_for_set_id)?
-			justification
+			.and_then(|justifications| justifications.into_justification(GRANDPA_ENGINE_ID))
+		{
+			grandpa_justification
 		} else {
 			trace!(
 				target: "afg",
@@ -257,7 +259,7 @@ pub trait ProvableJustification<Header: HeaderT>: Encode + Decode {
 
 	/// Decode and verify justification.
 	fn decode_and_verify(
-		justification: &Justification,
+		justification: &EncodedJustification,
 		set_id: u64,
 		authorities: &[(AuthorityId, u64)],
 	) -> ClientResult<Self> {
@@ -286,6 +288,7 @@ pub(crate) mod tests {
 	use super::*;
 	use crate::authorities::AuthoritySetChanges;
 	use sp_core::crypto::Public;
+	use sp_runtime::Justifications;
 	use sp_finality_grandpa::AuthorityList;
 	use sc_client_api::NewBlockState;
 	use sc_client_api::in_mem::Blockchain as InMemoryBlockchain;
@@ -330,31 +333,27 @@ pub(crate) mod tests {
 	}
 
 	fn test_blockchain() -> InMemoryBlockchain<Block> {
+		use sp_finality_grandpa::GRANDPA_ENGINE_ID as ID;
 		let blockchain = InMemoryBlockchain::<Block>::new();
-		blockchain
+		let just0 = Some(Justifications::from((ID, vec![0])));
-			.insert(header(0).hash(), header(0), Some(vec![0]), None, NewBlockState::Final)
+		let just1 = Some(Justifications::from((ID, vec![1])));
-			.unwrap();
+		let just2 = None;
-		blockchain
+		let just3 = Some(Justifications::from((ID, vec![3])));
-			.insert(header(1).hash(), header(1), Some(vec![1]), None, NewBlockState::Final)
+		blockchain.insert(header(0).hash(), header(0), just0, None, NewBlockState::Final).unwrap();
-			.unwrap();
+		blockchain.insert(header(1).hash(), header(1), just1, None, NewBlockState::Final).unwrap();
-		blockchain
+		blockchain.insert(header(2).hash(), header(2), just2, None, NewBlockState::Best).unwrap();
-			.insert(header(2).hash(), header(2), None, None, NewBlockState::Best)
+		blockchain.insert(header(3).hash(), header(3), just3, None, NewBlockState::Final).unwrap();
-			.unwrap();
-		blockchain
-			.insert(header(3).hash(), header(3), Some(vec![3]), None, NewBlockState::Final)
-			.unwrap();
 		blockchain
 	}
 
 	#[test]
 	fn finality_proof_fails_if_no_more_last_finalized_blocks() {
+		use sp_finality_grandpa::GRANDPA_ENGINE_ID as ID;
 		let blockchain = test_blockchain();
-		blockchain
+		let just1 = Some(Justifications::from((ID, vec![1])));
-			.insert(header(4).hash(), header(4), Some(vec![1]), None, NewBlockState::Best)
+		let just2 = Some(Justifications::from((ID, vec![2])));
-			.unwrap();
+		blockchain.insert(header(4).hash(), header(4), just1, None, NewBlockState::Best).unwrap();
-		blockchain
+		blockchain.insert(header(5).hash(), header(5), just2, None, NewBlockState::Best).unwrap();
-			.insert(header(5).hash(), header(5), Some(vec![2]), None, NewBlockState::Best)
-			.unwrap();
 
 		let mut authority_set_changes = AuthoritySetChanges::empty();
 		authority_set_changes.append(0, 5);
@@ -430,22 +429,17 @@ pub(crate) mod tests {
 
 	#[test]
 	fn finality_proof_using_authority_set_changes_fails_with_undefined_start() {
+		use sp_finality_grandpa::GRANDPA_ENGINE_ID as ID;
 		let blockchain = test_blockchain();
 		let auth = vec![(AuthorityId::from_slice(&[1u8; 32]), 1u64)];
-		let just4 = TestJustification((0, auth.clone()), vec![4]).encode();
+		let grandpa_just4 = TestJustification((0, auth.clone()), vec![4]).encode();
-		let just7 = TestJustification((1, auth.clone()), vec![7]).encode();
+		let grandpa_just7 = TestJustification((1, auth.clone()), vec![7]).encode();
-		blockchain
+		let just4 = Some(Justifications::from((ID, grandpa_just4)));
-			.insert(header(4).hash(), header(4), Some(just4), None, NewBlockState::Final)
+		let just7 = Some(Justifications::from((ID, grandpa_just7)));
-			.unwrap();
+		blockchain.insert(header(4).hash(), header(4), just4, None, NewBlockState::Final).unwrap();
-		blockchain
+		blockchain.insert(header(5).hash(), header(5), None, None, NewBlockState::Final).unwrap();
-			.insert(header(5).hash(), header(5), None, None, NewBlockState::Final)
+		blockchain.insert(header(6).hash(), header(6), None, None, NewBlockState::Final).unwrap();
-			.unwrap();
+		blockchain.insert(header(7).hash(), header(7), just7, None, NewBlockState::Final).unwrap();
-		blockchain
-			.insert(header(6).hash(), header(6), None, None, NewBlockState::Final)
-			.unwrap();
-		blockchain
-			.insert(header(7).hash(), header(7), Some(just7.clone()), None, NewBlockState::Final)
-			.unwrap();
 
 		// We have stored the correct block number for the relevant set, but as we are missing the
 		// block for the preceding set the start is not well-defined.
@@ -462,22 +456,17 @@ pub(crate) mod tests {
 
 	#[test]
 	fn finality_proof_using_authority_set_changes_works() {
+		use sp_finality_grandpa::GRANDPA_ENGINE_ID as ID;
 		let blockchain = test_blockchain();
 		let auth = vec![(AuthorityId::from_slice(&[1u8; 32]), 1u64)];
-		let just4 = TestJustification((0, auth.clone()), vec![4]).encode();
+		let grandpa_just4 = TestJustification((0, auth.clone()), vec![4]).encode();
-		let just7 = TestJustification((1, auth.clone()), vec![7]).encode();
+		let grandpa_just7 = TestJustification((1, auth.clone()), vec![7]).encode();
-		blockchain
+		let just4 = Some(Justifications::from((ID, grandpa_just4)));
-			.insert(header(4).hash(), header(4), Some(just4), None, NewBlockState::Final)
+		let just7 = Some(Justifications::from((ID, grandpa_just7.clone())));
-			.unwrap();
+		blockchain.insert(header(4).hash(), header(4), just4, None, NewBlockState::Final) .unwrap();
-		blockchain
+		blockchain.insert(header(5).hash(), header(5), None, None, NewBlockState::Final) .unwrap();
-			.insert(header(5).hash(), header(5), None, None, NewBlockState::Final)
+		blockchain.insert(header(6).hash(), header(6), None, None, NewBlockState::Final).unwrap();
-			.unwrap();
+		blockchain.insert(header(7).hash(), header(7), just7, None, NewBlockState::Final).unwrap();
-		blockchain
-			.insert(header(6).hash(), header(6), None, None, NewBlockState::Final)
-			.unwrap();
-		blockchain
-			.insert(header(7).hash(), header(7), Some(just7.clone()), None, NewBlockState::Final)
-			.unwrap();
 
 		let mut authority_set_changes = AuthoritySetChanges::empty();
 		authority_set_changes.append(0, 4);
@@ -497,7 +486,7 @@ pub(crate) mod tests {
 			proof_of_5,
 			FinalityProof {
 				block: header(7).hash(),
-				justification: just7,
+				justification: grandpa_just7,
 				unknown_headers: vec![header(6)],
 			}
 		);

substrate/client/finality-grandpa/src/import.rs

@@ -451,7 +451,7 @@ impl<BE, Block: BlockT, Client, SC> BlockImport<Block>
 		let pending_changes = self.make_authorities_changes(&mut block, hash, initial_sync)?;
 
 		// we don't want to finalize on `inner.import_block`
-		let mut justification = block.justification.take();
+		let mut justifications = block.justifications.take();
 		let import_result = (&*self.inner).import_block(block, new_cache);
 
 		let mut imported_aux = {
@@ -513,17 +513,20 @@ impl<BE, Block: BlockT, Client, SC> BlockImport<Block>
 				// 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.
-				justification.take();
+				justifications.take();
 			},
 			_ => {},
 		}
 
-		match justification {
+		let grandpa_justification = justifications
+			.and_then(|just| just.into_justification(GRANDPA_ENGINE_ID));
+
+		match grandpa_justification {
 			Some(justification) => {
 				let import_res = self.import_justification(
 					hash,
 					number,
-					justification,
+					(GRANDPA_ENGINE_ID, justification),
 					needs_justification,
 					initial_sync,
 				);
@@ -637,8 +640,14 @@ where
 		enacts_change: bool,
 		initial_sync: bool,
 	) -> Result<(), ConsensusError> {
+		if justification.0 != GRANDPA_ENGINE_ID {
+			return Err(ConsensusError::ClientImport(
+				"GRANDPA can only import GRANDPA Justifications.".into(),
+			));
+		}
+
 		let justification = GrandpaJustification::decode_and_verify_finalizes(
-			&justification,
+			&justification.1,
 			(hash, number),
 			self.authority_set.set_id(),
 			&self.authority_set.current_authorities(),

substrate/client/finality-grandpa/src/tests.rs

@@ -39,7 +39,7 @@ use sp_consensus::{
 	import_queue::BoxJustificationImport,
 };
 use std::{collections::{HashMap, HashSet}, pin::Pin};
-use sp_runtime::traits::{Block as BlockT, Header as HeaderT};
+use sp_runtime::{Justifications, traits::{Block as BlockT, Header as HeaderT}};
 use sp_runtime::generic::{BlockId, DigestItem};
 use sp_core::H256;
 use sp_keystore::{SyncCryptoStorePtr, SyncCryptoStore};
@@ -369,7 +369,7 @@ fn finalize_3_voters_no_observers() {
 
 	// normally there's no justification for finalized blocks
 	assert!(
-		net.lock().peer(0).client().justification(&BlockId::Number(20)).unwrap().is_none(),
+		net.lock().peer(0).client().justifications(&BlockId::Number(20)).unwrap().is_none(),
 		"Extra justification for block#1",
 	);
 }
@@ -613,7 +613,7 @@ fn justification_is_generated_periodically() {
 	// when block#32 (justification_period) is finalized, justification
 	// is required => generated
 	for i in 0..3 {
-		assert!(net.lock().peer(i).client().justification(&BlockId::Number(32)).unwrap().is_some());
+		assert!(net.lock().peer(i).client().justifications(&BlockId::Number(32)).unwrap().is_some());
 	}
 }
 
@@ -658,12 +658,12 @@ fn sync_justifications_on_change_blocks() {
 	// the first 3 peers are grandpa voters and therefore have already finalized
 	// block 21 and stored a justification
 	for i in 0..3 {
-		assert!(net.lock().peer(i).client().justification(&BlockId::Number(21)).unwrap().is_some());
+		assert!(net.lock().peer(i).client().justifications(&BlockId::Number(21)).unwrap().is_some());
 	}
 
 	// the last peer should get the justification by syncing from other peers
 	futures::executor::block_on(futures::future::poll_fn(move |cx| {
-		if net.lock().peer(3).client().justification(&BlockId::Number(21)).unwrap().is_none() {
+		if net.lock().peer(3).client().justifications(&BlockId::Number(21)).unwrap().is_none() {
 			net.lock().poll(cx);
 			Poll::Pending
 		} else {
@@ -868,7 +868,7 @@ fn test_bad_justification() {
 	let block = || {
 		let block = block.clone();
 		let mut import = BlockImportParams::new(BlockOrigin::File, block.header);
-		import.justification = Some(Vec::new());
+		import.justifications = Some(Justifications::from((GRANDPA_ENGINE_ID, Vec::new())));
 		import.body = Some(block.extrinsics);
 		import.fork_choice = Some(ForkChoiceStrategy::LongestChain);
 
@@ -1583,7 +1583,7 @@ fn imports_justification_for_regular_blocks_on_import() {
 
 	// we import the block with justification attached
 	let mut import = BlockImportParams::new(BlockOrigin::File, block.header);
-	import.justification = Some(justification.encode());
+	import.justifications = Some((GRANDPA_ENGINE_ID, justification.encode()).into());
 	import.body = Some(block.extrinsics);
 	import.fork_choice = Some(ForkChoiceStrategy::LongestChain);
 
@@ -1600,7 +1600,7 @@ fn imports_justification_for_regular_blocks_on_import() {
 
 	// the justification should be imported and available from the client
 	assert!(
-		client.justification(&BlockId::Hash(block_hash)).unwrap().is_some(),
+		client.justifications(&BlockId::Hash(block_hash)).unwrap().is_some(),
 	);
 }
 

substrate/client/light/src/backend.rs

@@ -32,7 +32,7 @@ use sp_state_machine::{
 	Backend as StateBackend, TrieBackend, InMemoryBackend, ChangesTrieTransaction,
 	StorageCollection, ChildStorageCollection,
 };
-use sp_runtime::{generic::BlockId, Justification, Storage};
+use sp_runtime::{generic::BlockId, Justification, Justifications, Storage};
 use sp_runtime::traits::{Block as BlockT, NumberFor, Zero, Header, HashFor};
 use sp_blockchain::{Error as ClientError, Result as ClientResult};
 use sc_client_api::{
@@ -199,6 +199,14 @@ impl<S, Block> ClientBackend<Block> for Backend<S, HashFor<Block>>
 		self.blockchain.storage().finalize_header(block)
 	}
 
+	fn append_justification(
+		&self,
+		_block: BlockId<Block>,
+		_justification: Justification,
+	) -> ClientResult<()> {
+		Ok(())
+	}
+
 	fn blockchain(&self) -> &Blockchain<S> {
 		&self.blockchain
 	}
@@ -278,7 +286,7 @@ impl<S, Block> BlockImportOperation<Block> for ImportOperation<Block, S>
 		&mut self,
 		header: Block::Header,
 		_body: Option<Vec<Block::Extrinsic>>,
-		_justification: Option<Justification>,
+		_justifications: Option<Justifications>,
 		state: NewBlockState,
 	) -> ClientResult<()> {
 		self.leaf_state = state;
@@ -356,7 +364,7 @@ impl<S, Block> BlockImportOperation<Block> for ImportOperation<Block, S>
 	fn mark_finalized(
 		&mut self,
 		block: BlockId<Block>,
-		_justification: Option<Justification>,
+		_justifications: Option<Justification>,
 	) -> ClientResult<()> {
 		self.finalized_blocks.push(block);
 		Ok(())

substrate/client/light/src/blockchain.rs

@@ -21,7 +21,7 @@
 
 use std::sync::Arc;
 
-use sp_runtime::{Justification, generic::BlockId};
+use sp_runtime::{Justifications, generic::BlockId};
 use sp_runtime::traits::{Block as BlockT, Header as HeaderT, NumberFor, Zero};
 
 use sp_blockchain::{
@@ -109,7 +109,7 @@ impl<S, Block> BlockchainBackend<Block> for Blockchain<S> where Block: BlockT, S
 		Err(ClientError::NotAvailableOnLightClient)
 	}
 
-	fn justification(&self, _id: BlockId<Block>) -> ClientResult<Option<Justification>> {
+	fn justifications(&self, _id: BlockId<Block>) -> ClientResult<Option<Justifications>> {
 		Err(ClientError::NotAvailableOnLightClient)
 	}
 

substrate/client/network/src/behaviour.rs

@@ -37,7 +37,7 @@ use libp2p::swarm::{
 use log::debug;
 use prost::Message;
 use sp_consensus::{BlockOrigin, import_queue::{IncomingBlock, Origin}};
-use sp_runtime::{traits::{Block as BlockT, NumberFor}, Justification};
+use sp_runtime::{traits::{Block as BlockT, NumberFor}, Justifications};
 use std::{
 	borrow::Cow,
 	collections::{HashSet, VecDeque},
@@ -84,7 +84,7 @@ pub struct Behaviour<B: BlockT> {
 /// Event generated by `Behaviour`.
 pub enum BehaviourOut<B: BlockT> {
 	BlockImport(BlockOrigin, Vec<IncomingBlock<B>>),
-	JustificationImport(Origin, B::Hash, NumberFor<B>, Justification),
+	JustificationImport(Origin, B::Hash, NumberFor<B>, Justifications),
 
 	/// Started a random iterative Kademlia discovery query.
 	RandomKademliaStarted(ProtocolId),

substrate/client/network/src/block_request_handler.rs

@@ -275,12 +275,28 @@ impl<B: BlockT> BlockRequestHandler<B> {
 			let number = *header.number();
 			let hash = header.hash();
 			let parent_hash = *header.parent_hash();
-			let justification = if get_justification {
+			let justifications = if get_justification {
-				self.client.justification(&BlockId::Hash(hash))?
+				self.client.justifications(&BlockId::Hash(hash))?
 			} else {
 				None
 			};
-			let is_empty_justification = justification.as_ref().map(|j| j.is_empty()).unwrap_or(false);
+
+			// TODO: In a follow up PR tracked by https://github.com/paritytech/substrate/issues/8172
+			// we want to send/receive all justifications.
+			// For now we keep compatibility by selecting precisely the GRANDPA one, and not just
+			// the first one. When sending we could have just taken the first one, since we don't
+			// expect there to be any other kind currently, but when receiving we need to add the
+			// engine ID tag.
+			// The ID tag is hardcoded here to avoid depending on the GRANDPA crate, and will be
+			// removed when resolving the above issue.
+			let justification = justifications.and_then(|just| just.into_justification(*b"FRNK"));
+
+			let is_empty_justification = justification
+				.as_ref()
+				.map(|j| j.is_empty())
+				.unwrap_or(false);
+
+			let justification = justification.unwrap_or_default();
 
 			let body = if get_body {
 				match self.client.block_body(&BlockId::Hash(hash))? {
@@ -306,7 +322,7 @@ impl<B: BlockT> BlockRequestHandler<B> {
 				body,
 				receipt: Vec::new(),
 				message_queue: Vec::new(),
-				justification: justification.unwrap_or_default(),
+				justification,
 				is_empty_justification,
 			};
 

substrate/client/network/src/gossip/tests.rs

@@ -52,7 +52,7 @@ fn build_test_full_node(network_config: config::NetworkConfiguration)
 			&mut self,
 			origin: sp_consensus::BlockOrigin,
 			header: B::Header,
-			justification: Option<sp_runtime::Justification>,
+			justifications: Option<sp_runtime::Justifications>,
 			body: Option<Vec<B::Extrinsic>>,
 		) -> Result<
 			(
@@ -79,7 +79,7 @@ fn build_test_full_node(network_config: config::NetworkConfiguration)
 			let mut import = sp_consensus::BlockImportParams::new(origin, header);
 			import.body = body;
 			import.finalized = self.0;
-			import.justification = justification;
+			import.justifications = justifications;
 			import.fork_choice = Some(sp_consensus::ForkChoiceStrategy::LongestChain);
 			Ok((import, maybe_keys))
 		}

substrate/client/network/src/protocol.rs

@@ -43,9 +43,10 @@ use sp_consensus::{
 	block_validation::BlockAnnounceValidator,
 	import_queue::{BlockImportResult, BlockImportError, IncomingBlock, Origin}
 };
-use sp_runtime::{generic::BlockId, Justification};
+use sp_runtime::{
-use sp_runtime::traits::{
+	Justifications,
-	Block as BlockT, Header as HeaderT, NumberFor, Zero, CheckedSub
+	generic::BlockId,
+	traits::{Block as BlockT, Header as HeaderT, NumberFor, Zero, CheckedSub},
 };
 use sp_arithmetic::traits::SaturatedConversion;
 use sync::{ChainSync, SyncState};
@@ -612,8 +613,8 @@ impl<B: BlockT> Protocol<B> {
 		if request.fields == message::BlockAttributes::JUSTIFICATION {
 			match self.sync.on_block_justification(peer_id, block_response) {
 				Ok(sync::OnBlockJustification::Nothing) => CustomMessageOutcome::None,
-				Ok(sync::OnBlockJustification::Import { peer, hash, number, justification }) =>
+				Ok(sync::OnBlockJustification::Import { peer, hash, number, justifications }) =>
-					CustomMessageOutcome::JustificationImport(peer, hash, number, justification),
+					CustomMessageOutcome::JustificationImport(peer, hash, number, justifications),
 				Err(sync::BadPeer(id, repu)) => {
 					self.behaviour.disconnect_peer(&id, HARDCODED_PEERSETS_SYNC);
 					self.peerset_handle.report_peer(id, repu);
@@ -1134,7 +1135,7 @@ fn prepare_block_request<B: BlockT>(
 #[must_use]
 pub enum CustomMessageOutcome<B: BlockT> {
 	BlockImport(BlockOrigin, Vec<IncomingBlock<B>>),
-	JustificationImport(Origin, B::Hash, NumberFor<B>, Justification),
+	JustificationImport(Origin, B::Hash, NumberFor<B>, Justifications),
 	/// Notification protocols have been opened with a remote.
 	NotificationStreamOpened {
 		remote: PeerId,

substrate/client/network/src/protocol/message.rs

@@ -148,7 +148,7 @@ pub struct RemoteReadResponse {
 pub mod generic {
 	use bitflags::bitflags;
 	use codec::{Encode, Decode, Input, Output};
-	use sp_runtime::Justification;
+	use sp_runtime::EncodedJustification;
 	use super::{
 		RemoteReadResponse, Transactions, Direction,
 		RequestId, BlockAttributes, RemoteCallResponse, ConsensusEngineId,
@@ -233,7 +233,7 @@ pub mod generic {
 		/// Block message queue if requested.
 		pub message_queue: Option<Vec<u8>>,
 		/// Justification if requested.
-		pub justification: Option<Justification>,
+		pub justification: Option<EncodedJustification>,
 	}
 
 	/// Identifies starting point of a block sequence.

substrate/client/network/src/protocol/sync.rs

@@ -44,7 +44,7 @@ use extra_requests::ExtraRequests;
 use libp2p::PeerId;
 use log::{debug, trace, warn, info, error};
 use sp_runtime::{
-	Justification,
+	EncodedJustification, Justifications,
 	generic::BlockId,
 	traits::{
 		Block as BlockT, Header as HeaderT, NumberFor, Zero, One, CheckedSub, SaturatedConversion,
@@ -425,7 +425,7 @@ pub enum OnBlockJustification<B: BlockT> {
 		peer: PeerId,
 		hash: B::Hash,
 		number: NumberFor<B>,
-		justification: Justification
+		justifications: Justifications
 	}
 }
 
@@ -823,11 +823,13 @@ impl<B: BlockT> ChainSync<B> {
 								.drain(self.best_queued_number + One::one())
 								.into_iter()
 								.map(|block_data| {
+									let justifications =
+										legacy_justification_mapping(block_data.block.justification);
 									IncomingBlock {
 										hash: block_data.block.hash,
 										header: block_data.block.header,
 										body: block_data.block.body,
-										justification: block_data.block.justification,
+										justifications,
 										origin: block_data.origin,
 										allow_missing_state: true,
 										import_existing: false,
@@ -846,7 +848,7 @@ impl<B: BlockT> ChainSync<B> {
 									hash: b.hash,
 									header: b.header,
 									body: b.body,
-									justification: b.justification,
+									justifications: legacy_justification_mapping(b.justification),
 									origin: Some(who.clone()),
 									allow_missing_state: true,
 									import_existing: false,
@@ -955,7 +957,7 @@ impl<B: BlockT> ChainSync<B> {
 							hash: b.hash,
 							header: b.header,
 							body: b.body,
-							justification: b.justification,
+							justifications: legacy_justification_mapping(b.justification),
 							origin: Some(who.clone()),
 							allow_missing_state: true,
 							import_existing: false,
@@ -1039,8 +1041,11 @@ impl<B: BlockT> ChainSync<B> {
 				None
 			};
 
-			if let Some((peer, hash, number, j)) = self.extra_justifications.on_response(who, justification) {
+			if let Some((peer, hash, number, j)) = self
-				return Ok(OnBlockJustification::Import { peer, hash, number, justification: j })
+				.extra_justifications
+				.on_response(who, legacy_justification_mapping(justification))
+			{
+				return Ok(OnBlockJustification::Import { peer, hash, number, justifications: j })
 			}
 		}
 
@@ -1597,6 +1602,14 @@ impl<B: BlockT> ChainSync<B> {
 	}
 }
 
+// This is purely during a backwards compatible transitionary period and should be removed
+// once we can assume all nodes can send and receive multiple Justifications
+// The ID tag is hardcoded here to avoid depending on the GRANDPA crate.
+// TODO: https://github.com/paritytech/substrate/issues/8172
+fn legacy_justification_mapping(justification: Option<EncodedJustification>) -> Option<Justifications> {
+	justification.map(|just| (*b"FRNK", just).into())
+}
+
 #[derive(Debug)]
 pub(crate) struct Metrics {
 	pub(crate) queued_blocks: u32,
@@ -2396,7 +2409,8 @@ mod test {
 		);
 
 		let finalized_block = blocks[MAX_BLOCKS_TO_LOOK_BACKWARDS as usize * 2 - 1].clone();
-		client.finalize_block(BlockId::Hash(finalized_block.hash()), Some(Vec::new())).unwrap();
+		let just = (*b"TEST", Vec::new());
+		client.finalize_block(BlockId::Hash(finalized_block.hash()), Some(just)).unwrap();
 		sync.update_chain_info(&info.best_hash, info.best_number);
 
 		let peer_id1 = PeerId::random();

substrate/client/network/src/service.rs

@@ -1452,11 +1452,11 @@ impl<B: BlockT + 'static, H: ExHashT> Future for NetworkWorker<B, H> {
 					}
 					this.import_queue.import_blocks(origin, blocks);
 				},
-				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::JustificationImport(origin, hash, nb, justification))) => {
+				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::JustificationImport(origin, hash, nb, justifications))) => {
 					if let Some(metrics) = this.metrics.as_ref() {
 						metrics.import_queue_justifications_submitted.inc();
 					}
-					this.import_queue.import_justification(origin, hash, nb, justification);
+					this.import_queue.import_justifications(origin, hash, nb, justifications);
 				},
 				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::InboundRequest { protocol, result, .. })) => {
 					if let Some(metrics) = this.metrics.as_ref() {

substrate/client/network/src/service/tests.rs

@@ -52,7 +52,7 @@ fn build_test_full_node(config: config::NetworkConfiguration)
 			&mut self,
 			origin: sp_consensus::BlockOrigin,
 			header: B::Header,
-			justification: Option<sp_runtime::Justification>,
+			justifications: Option<sp_runtime::Justifications>,
 			body: Option<Vec<B::Extrinsic>>,
 		) -> Result<
 			(
@@ -79,7 +79,7 @@ fn build_test_full_node(config: config::NetworkConfiguration)
 			let mut import = sp_consensus::BlockImportParams::new(origin, header);
 			import.body = body;
 			import.finalized = self.0;
-			import.justification = justification;
+			import.justifications = justifications;
 			import.fork_choice = Some(sp_consensus::ForkChoiceStrategy::LongestChain);
 			Ok((import, maybe_keys))
 		}

substrate/client/network/test/src/block_import.rs

@@ -35,13 +35,13 @@ fn prepare_good_block() -> (TestClient, Hash, u64, PeerId, IncomingBlock<Block>)
 
 	let (hash, number) = (client.block_hash(1).unwrap().unwrap(), 1);
 	let header = client.header(&BlockId::Number(1)).unwrap();
-	let justification = client.justification(&BlockId::Number(1)).unwrap();
+	let justifications = client.justifications(&BlockId::Number(1)).unwrap();
 	let peer_id = PeerId::random();
 	(client, hash, number, peer_id.clone(), IncomingBlock {
 		hash,
 		header,
 		body: Some(Vec::new()),
-		justification,
+		justifications,
 		origin: Some(peer_id.clone()),
 		allow_missing_state: false,
 		import_existing: false,

substrate/client/network/test/src/lib.rs

@@ -63,7 +63,7 @@ use sp_core::H256;
 use sc_network::config::ProtocolConfig;
 use sp_runtime::generic::{BlockId, OpaqueDigestItemId};
 use sp_runtime::traits::{Block as BlockT, Header as HeaderT, NumberFor};
-use sp_runtime::Justification;
+use sp_runtime::{Justification, Justifications};
 use substrate_test_runtime_client::{self, AccountKeyring};
 use sc_service::client::Client;
 pub use sc_network::config::EmptyTransactionPool;
@@ -109,7 +109,7 @@ impl<B: BlockT> Verifier<B> for PassThroughVerifier {
 		&mut self,
 		origin: BlockOrigin,
 		header: B::Header,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		body: Option<Vec<B::Extrinsic>>
 	) -> Result<(BlockImportParams<B, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String> {
 		let maybe_keys = header.digest()
@@ -120,7 +120,7 @@ impl<B: BlockT> Verifier<B> for PassThroughVerifier {
 		let mut import = BlockImportParams::new(origin, header);
 		import.body = body;
 		import.finalized = self.finalized;
-		import.justification = justification;
+		import.justifications = justifications;
 		import.fork_choice = Some(self.fork_choice.clone());
 
 		Ok((import, maybe_keys))
@@ -184,10 +184,10 @@ impl PeersClient {
 		}
 	}
 
-	pub fn justification(&self, block: &BlockId<Block>) -> ClientResult<Option<Justification>> {
+	pub fn justifications(&self, block: &BlockId<Block>) -> ClientResult<Option<Justifications>> {
 		match *self {
-			PeersClient::Full(ref client, ref _backend) => client.justification(block),
+			PeersClient::Full(ref client, ref _backend) => client.justifications(block),
-			PeersClient::Light(ref client, ref _backend) => client.justification(block),
+			PeersClient::Light(ref client, ref _backend) => client.justifications(block),
 		}
 	}
 
@@ -577,11 +577,11 @@ impl<B: BlockT> Verifier<B> for VerifierAdapter<B> {
 		&mut self,
 		origin: BlockOrigin,
 		header: B::Header,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		body: Option<Vec<B::Extrinsic>>
 	) -> Result<(BlockImportParams<B, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String> {
 		let hash = header.hash();
-		self.verifier.lock().verify(origin, header, justification, body).map_err(|e| {
+		self.verifier.lock().verify(origin, header, justifications, body).map_err(|e| {
 			self.failed_verifications.lock().insert(hash, e.clone());
 			e
 		})

substrate/client/network/test/src/sync.rs

@@ -22,6 +22,7 @@ use futures::{Future, executor::block_on};
 use super::*;
 use sp_consensus::block_validation::Validation;
 use substrate_test_runtime::Header;
+use sp_runtime::Justifications;
 
 fn test_ancestor_search_when_common_is(n: usize) {
 	sp_tracing::try_init_simple();
@@ -248,13 +249,14 @@ fn sync_justifications() {
 	net.block_until_sync();
 
 	// there's currently no justification for block #10
-	assert_eq!(net.peer(0).client().justification(&BlockId::Number(10)).unwrap(), None);
+	assert_eq!(net.peer(0).client().justifications(&BlockId::Number(10)).unwrap(), None);
-	assert_eq!(net.peer(1).client().justification(&BlockId::Number(10)).unwrap(), None);
+	assert_eq!(net.peer(1).client().justifications(&BlockId::Number(10)).unwrap(), None);
 
 	// we finalize block #10, #15 and #20 for peer 0 with a justification
-	net.peer(0).client().finalize_block(BlockId::Number(10), Some(Vec::new()), true).unwrap();
+	let just = (*b"FRNK", Vec::new());
-	net.peer(0).client().finalize_block(BlockId::Number(15), Some(Vec::new()), true).unwrap();
+	net.peer(0).client().finalize_block(BlockId::Number(10), Some(just.clone()), true).unwrap();
-	net.peer(0).client().finalize_block(BlockId::Number(20), Some(Vec::new()), true).unwrap();
+	net.peer(0).client().finalize_block(BlockId::Number(15), Some(just.clone()), true).unwrap();
+	net.peer(0).client().finalize_block(BlockId::Number(20), Some(just.clone()), true).unwrap();
 
 	let h1 = net.peer(1).client().header(&BlockId::Number(10)).unwrap().unwrap();
 	let h2 = net.peer(1).client().header(&BlockId::Number(15)).unwrap().unwrap();
@@ -269,10 +271,20 @@ fn sync_justifications() {
 		net.poll(cx);
 
 		for height in (10..21).step_by(5) {
-			if net.peer(0).client().justification(&BlockId::Number(height)).unwrap() != Some(Vec::new()) {
+			if net
+				.peer(0)
+				.client()
+				.justifications(&BlockId::Number(height))
+				.unwrap() != Some(Justifications::from((*b"FRNK", Vec::new())))
+			{
 				return Poll::Pending;
 			}
-			if net.peer(1).client().justification(&BlockId::Number(height)).unwrap() != Some(Vec::new()) {
+			if net
+				.peer(1)
+				.client()
+				.justifications(&BlockId::Number(height))
+				.unwrap() != Some(Justifications::from((*b"FRNK", Vec::new())))
+			{
 				return Poll::Pending;
 			}
 		}
@@ -295,7 +307,8 @@ fn sync_justifications_across_forks() {
 	// for both and finalize the small fork instead.
 	net.block_until_sync();
 
-	net.peer(0).client().finalize_block(BlockId::Hash(f1_best), Some(Vec::new()), true).unwrap();
+	let just = (*b"FRNK", Vec::new());
+	net.peer(0).client().finalize_block(BlockId::Hash(f1_best), Some(just), true).unwrap();
 
 	net.peer(1).request_justification(&f1_best, 10);
 	net.peer(1).request_justification(&f2_best, 11);
@@ -303,8 +316,16 @@ fn sync_justifications_across_forks() {
 	block_on(futures::future::poll_fn::<(), _>(|cx| {
 		net.poll(cx);
 
-		if net.peer(0).client().justification(&BlockId::Number(10)).unwrap() == Some(Vec::new()) &&
+		if net
-			net.peer(1).client().justification(&BlockId::Number(10)).unwrap() == Some(Vec::new())
+			.peer(0)
+			.client()
+			.justifications(&BlockId::Number(10))
+			.unwrap() == Some(Justifications::from((*b"FRNK", Vec::new())))
+			&& net
+				.peer(1)
+				.client()
+				.justifications(&BlockId::Number(10))
+				.unwrap() == Some(Justifications::from((*b"FRNK", Vec::new())))
 		{
 			Poll::Ready(())
 		} else {
@@ -696,8 +717,9 @@ fn can_sync_to_peers_with_wrong_common_block() {
 	net.block_until_connected();
 
 	// both peers re-org to the same fork without notifying each other
-	net.peer(0).client().finalize_block(BlockId::Hash(fork_hash), Some(Vec::new()), true).unwrap();
+	let just = Some((*b"FRNK", Vec::new()));
-	net.peer(1).client().finalize_block(BlockId::Hash(fork_hash), Some(Vec::new()), true).unwrap();
+	net.peer(0).client().finalize_block(BlockId::Hash(fork_hash), just.clone(), true).unwrap();
+	net.peer(1).client().finalize_block(BlockId::Hash(fork_hash), just, true).unwrap();
 	let final_hash = net.peer(0).push_blocks(1, false);
 
 	net.block_until_sync();
@@ -948,8 +970,8 @@ fn multiple_requests_are_accepted_as_long_as_they_are_not_fulfilled() {
 	net.block_until_sync();
 
 	// there's currently no justification for block #10
-	assert_eq!(net.peer(0).client().justification(&BlockId::Number(10)).unwrap(), None);
+	assert_eq!(net.peer(0).client().justifications(&BlockId::Number(10)).unwrap(), None);
-	assert_eq!(net.peer(1).client().justification(&BlockId::Number(10)).unwrap(), None);
+	assert_eq!(net.peer(1).client().justifications(&BlockId::Number(10)).unwrap(), None);
 
 	let h1 = net.peer(1).client().header(&BlockId::Number(10)).unwrap().unwrap();
 
@@ -967,12 +989,21 @@ fn multiple_requests_are_accepted_as_long_as_they_are_not_fulfilled() {
 	}
 
 	// Finalize the block and make the justification available.
-	net.peer(0).client().finalize_block(BlockId::Number(10), Some(Vec::new()), true).unwrap();
+	net.peer(0).client().finalize_block(
+		BlockId::Number(10),
+		Some((*b"FRNK", Vec::new())),
+		true,
+	).unwrap();
 
 	block_on(futures::future::poll_fn::<(), _>(|cx| {
 		net.poll(cx);
 
-		if net.peer(1).client().justification(&BlockId::Number(10)).unwrap() != Some(Vec::new()) {
+		if net
+			.peer(1)
+			.client()
+			.justifications(&BlockId::Number(10))
+			.unwrap() != Some(Justifications::from((*b"FRNK", Vec::new())))
+		{
 			return Poll::Pending;
 		}
 

substrate/client/rpc/src/chain/chain_light.rs

@@ -106,7 +106,7 @@ impl<Block, Client, F> ChainBackend<Client, Block> for LightChain<Block, Client,
 					.compat()
 					.map(move |body| Some(SignedBlock {
 						block: Block::new(header, body),
-						justification: None,
+						justifications: None,
 					}))
 					.map_err(client_err)
 				),

substrate/client/rpc/src/chain/tests.rs

@@ -72,7 +72,7 @@ fn should_return_a_block() {
 	// Genesis block is not justified
 	assert_matches!(
 		api.block(Some(client.genesis_hash()).into()).wait(),
-		Ok(Some(SignedBlock { justification: None, .. }))
+		Ok(Some(SignedBlock { justifications: None, .. }))
 	);
 
 	assert_matches!(

substrate/client/service/src/chain_ops/import_blocks.rs

@@ -168,7 +168,7 @@ fn import_block_to_queue<TBl, TImpQu>(
 			hash,
 			header: Some(header),
 			body: Some(extrinsics),
-			justification: signed_block.justification,
+			justifications: signed_block.justifications,
 			origin: None,
 			allow_missing_state: false,
 			import_existing: force,

substrate/client/service/src/client/client.rs

@@ -41,7 +41,7 @@ use sc_telemetry::{
 	SUBSTRATE_INFO,
 };
 use sp_runtime::{
-	Justification, BuildStorage,
+	Justification, Justifications, BuildStorage,
 	generic::{BlockId, SignedBlock, DigestItem},
 	traits::{
 		Block as BlockT, Header as HeaderT, Zero, NumberFor,
@@ -625,7 +625,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		let BlockImportParams {
 			origin,
 			header,
-			justification,
+			justifications,
 			post_digests,
 			body,
 			storage_changes,
@@ -637,7 +637,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			..
 		} = import_block;
 
-		assert!(justification.is_some() && finalized || justification.is_none());
+		assert!(justifications.is_some() && finalized || justifications.is_none());
 
 		if !intermediates.is_empty() {
 			return Err(Error::IncompletePipeline)
@@ -665,7 +665,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			origin,
 			hash,
 			import_headers,
-			justification,
+			justifications,
 			body,
 			storage_changes,
 			new_cache,
@@ -704,7 +704,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		origin: BlockOrigin,
 		hash: Block::Hash,
 		import_headers: PrePostHeader<Block::Header>,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		body: Option<Vec<Block::Extrinsic>>,
 		storage_changes: Option<sp_api::StorageChanges<backend::StateBackendFor<B, Block>, Block>>,
 		new_cache: HashMap<CacheKeyId, Vec<u8>>,
@@ -820,7 +820,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		operation.op.set_block_data(
 			import_headers.post().clone(),
 			body,
-			justification,
+			justifications,
 			leaf_state,
 		)?;
 
@@ -1926,9 +1926,9 @@ impl<B, E, Block, RA> BlockBackend<Block> for Client<B, E, Block, RA>
 	}
 
 	fn block(&self, id: &BlockId<Block>) -> sp_blockchain::Result<Option<SignedBlock<Block>>> {
-		Ok(match (self.header(id)?, self.body(id)?, self.justification(id)?) {
+		Ok(match (self.header(id)?, self.body(id)?, self.justifications(id)?) {
-			(Some(header), Some(extrinsics), justification) =>
+			(Some(header), Some(extrinsics), justifications) =>
-				Some(SignedBlock { block: Block::new(header, extrinsics), justification }),
+				Some(SignedBlock { block: Block::new(header, extrinsics), justifications }),
 			_ => None,
 		})
 	}
@@ -1937,8 +1937,8 @@ impl<B, E, Block, RA> BlockBackend<Block> for Client<B, E, Block, RA>
 		Client::block_status(self, id)
 	}
 
-	fn justification(&self, id: &BlockId<Block>) -> sp_blockchain::Result<Option<Justification>> {
+	fn justifications(&self, id: &BlockId<Block>) -> sp_blockchain::Result<Option<Justifications>> {
-		self.backend.blockchain().justification(*id)
+		self.backend.blockchain().justifications(*id)
 	}
 
 	fn block_hash(&self, number: NumberFor<Block>) -> sp_blockchain::Result<Option<Block::Hash>> {

substrate/client/service/test/src/client/light.rs

@@ -28,8 +28,9 @@ use sc_light::{
 };
 use std::sync::Arc;
 use sp_runtime::{
-	traits::{BlakeTwo256, HashFor, NumberFor},
+	generic::BlockId,
-	generic::BlockId, traits::{Block as _, Header as HeaderT}, Digest,
+	traits::{BlakeTwo256, Block as _, HashFor, Header as HeaderT, NumberFor},
+	Digest, Justifications,
 };
 use std::collections::HashMap;
 use parking_lot::Mutex;
@@ -377,7 +378,7 @@ fn execution_proof_is_generated_and_checked() {
 		remote_client.import_justified(
 			BlockOrigin::Own,
 			remote_client.new_block(digest).unwrap().build().unwrap().block,
-			Default::default(),
+			Justifications::from((*b"TEST", Default::default())),
 		).unwrap();
 	}
 

substrate/client/service/test/src/client/mod.rs

@@ -36,8 +36,9 @@ use sc_client_db::{
 };
 use sc_block_builder::BlockBuilderProvider;
 use sc_service::client::{self, Client, LocalCallExecutor, new_in_mem};
-use sp_runtime::traits::{
+use sp_runtime::{
-	BlakeTwo256, Block as BlockT, Header as HeaderT,
+	ConsensusEngineId,
+	traits::{BlakeTwo256, Block as BlockT, Header as HeaderT},
 };
 use substrate_test_runtime::TestAPI;
 use sp_state_machine::backend::Backend as _;
@@ -51,12 +52,14 @@ use sp_consensus::{
 };
 use sp_storage::StorageKey;
 use sp_trie::{TrieConfiguration, trie_types::Layout};
-use sp_runtime::{generic::BlockId, DigestItem};
+use sp_runtime::{generic::BlockId, DigestItem, Justifications};
 use hex_literal::hex;
 
 mod light;
 mod db;
 
+const TEST_ENGINE_ID: ConsensusEngineId = *b"TEST";
+
 native_executor_instance!(
 	Executor,
 	substrate_test_runtime_client::runtime::api::dispatch,
@@ -1016,7 +1019,7 @@ fn import_with_justification() {
 	client.import(BlockOrigin::Own, a2.clone()).unwrap();
 
 	// A2 -> A3
-	let justification = vec![1, 2, 3];
+	let justification = Justifications::from((TEST_ENGINE_ID, vec![1, 2, 3]));
 	let a3 = client.new_block_at(
 		&BlockId::Hash(a2.hash()),
 		Default::default(),
@@ -1030,17 +1033,17 @@ fn import_with_justification() {
 	);
 
 	assert_eq!(
-		client.justification(&BlockId::Hash(a3.hash())).unwrap(),
+		client.justifications(&BlockId::Hash(a3.hash())).unwrap(),
 		Some(justification),
 	);
 
 	assert_eq!(
-		client.justification(&BlockId::Hash(a1.hash())).unwrap(),
+		client.justifications(&BlockId::Hash(a1.hash())).unwrap(),
 		None,
 	);
 
 	assert_eq!(
-		client.justification(&BlockId::Hash(a2.hash())).unwrap(),
+		client.justifications(&BlockId::Hash(a2.hash())).unwrap(),
 		None,
 	);
 }
@@ -1088,7 +1091,7 @@ fn importing_diverged_finalized_block_should_trigger_reorg() {
 	);
 
 	// importing B1 as finalized should trigger a re-org and set it as new best
-	let justification = vec![1, 2, 3];
+	let justification = Justifications::from((TEST_ENGINE_ID, vec![1, 2, 3]));
 	client.import_justified(BlockOrigin::Own, b1.clone(), justification).unwrap();
 
 	assert_eq!(

substrate/primitives/blockchain/src/backend.rs

@@ -21,7 +21,7 @@ use std::sync::Arc;
 
 use sp_runtime::traits::{Block as BlockT, Header as HeaderT, NumberFor};
 use sp_runtime::generic::BlockId;
-use sp_runtime::Justification;
+use sp_runtime::Justifications;
 use log::warn;
 use parking_lot::RwLock;
 
@@ -84,8 +84,8 @@ pub trait HeaderBackend<Block: BlockT>: Send + Sync {
 pub trait Backend<Block: BlockT>: HeaderBackend<Block> + HeaderMetadata<Block, Error=Error> {
 	/// Get block body. Returns `None` if block is not found.
 	fn body(&self, id: BlockId<Block>) -> Result<Option<Vec<<Block as BlockT>::Extrinsic>>>;
-	/// Get block justification. Returns `None` if justification does not exist.
+	/// Get block justifications. Returns `None` if no justification exists.
-	fn justification(&self, id: BlockId<Block>) -> Result<Option<Justification>>;
+	fn justifications(&self, id: BlockId<Block>) -> Result<Option<Justifications>>;
 	/// Get last finalized block hash.
 	fn last_finalized(&self) -> Result<Block::Hash>;
 	/// Returns data cache reference, if it is enabled on this backend.

substrate/primitives/consensus/common/src/block_import.rs

@@ -18,7 +18,7 @@
 //! Block import helpers.
 
 use sp_runtime::traits::{Block as BlockT, DigestItemFor, Header as HeaderT, NumberFor, HashFor};
-use sp_runtime::Justification;
+use sp_runtime::{Justification, Justifications};
 use serde::{Serialize, Deserialize};
 use std::borrow::Cow;
 use std::collections::HashMap;
@@ -128,8 +128,8 @@ pub struct BlockImportParams<Block: BlockT, Transaction> {
 	/// re-executed in a runtime that checks digest equivalence -- the
 	/// post-runtime digests are pushed back on after.
 	pub header: Block::Header,
-	/// Justification provided for this block from the outside.
+	/// Justification(s) provided for this block from the outside.
-	pub justification: Option<Justification>,
+	pub justifications: Option<Justifications>,
 	/// Digest items that have been added after the runtime for external
 	/// work, like a consensus signature.
 	pub post_digests: Vec<DigestItemFor<Block>>,
@@ -174,7 +174,7 @@ impl<Block: BlockT, Transaction> BlockImportParams<Block, Transaction> {
 	) -> Self {
 		Self {
 			origin, header,
-			justification: None,
+			justifications: None,
 			post_digests: Vec::new(),
 			body: None,
 			storage_changes: None,
@@ -219,7 +219,7 @@ impl<Block: BlockT, Transaction> BlockImportParams<Block, Transaction> {
 		BlockImportParams {
 			origin: self.origin,
 			header: self.header,
-			justification: self.justification,
+			justifications: self.justifications,
 			post_digests: self.post_digests,
 			body: self.body,
 			storage_changes: None,

substrate/primitives/consensus/common/src/import_queue.rs

@@ -28,7 +28,7 @@
 
 use std::collections::HashMap;
 
-use sp_runtime::{Justification, traits::{Block as BlockT, Header as _, NumberFor}};
+use sp_runtime::{Justifications, traits::{Block as BlockT, Header as _, NumberFor}};
 
 use crate::{
 	error::Error as ConsensusError,
@@ -68,8 +68,8 @@ pub struct IncomingBlock<B: BlockT> {
 	pub header: Option<<B as BlockT>::Header>,
 	/// Block body if requested.
 	pub body: Option<Vec<<B as BlockT>::Extrinsic>>,
-	/// Justification if requested.
+	/// Justification(s) if requested.
-	pub justification: Option<Justification>,
+	pub justifications: Option<Justifications>,
 	/// The peer, we received this from
 	pub origin: Option<Origin>,
 	/// Allow importing the block skipping state verification if parent state is missing.
@@ -90,7 +90,7 @@ pub trait Verifier<B: BlockT>: Send + Sync {
 		&mut self,
 		origin: BlockOrigin,
 		header: B::Header,
-		justification: Option<Justification>,
+		justifications: Option<Justifications>,
 		body: Option<Vec<B::Extrinsic>>,
 	) -> Result<(BlockImportParams<B, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String>;
 }
@@ -102,13 +102,13 @@ pub trait Verifier<B: BlockT>: Send + Sync {
 pub trait ImportQueue<B: BlockT>: Send {
 	/// Import bunch of blocks.
 	fn import_blocks(&mut self, origin: BlockOrigin, blocks: Vec<IncomingBlock<B>>);
-	/// Import a block justification.
+	/// Import block justifications.
-	fn import_justification(
+	fn import_justifications(
 		&mut self,
 		who: Origin,
 		hash: B::Hash,
 		number: NumberFor<B>,
-		justification: Justification
+		justifications: Justifications
 	);
 	/// Polls for actions to perform on the network.
 	///
@@ -182,8 +182,8 @@ pub(crate) fn import_single_block_metered<B: BlockT, V: Verifier<B>, Transaction
 ) -> Result<BlockImportResult<NumberFor<B>>, BlockImportError> {
 	let peer = block.origin;
 
-	let (header, justification) = match (block.header, block.justification) {
+	let (header, justifications) = match (block.header, block.justifications) {
-		(Some(header), justification) => (header, justification),
+		(Some(header), justifications) => (header, justifications),
 		(None, _) => {
 			if let Some(ref peer) = peer {
 				debug!(target: "sync", "Header {} was not provided by {} ", block.hash, peer);
@@ -238,7 +238,7 @@ pub(crate) fn import_single_block_metered<B: BlockT, V: Verifier<B>, Transaction
 	}
 
 	let started = wasm_timer::Instant::now();
-	let (mut import_block, maybe_keys) = verifier.verify(block_origin, header, justification, block.body)
+	let (mut import_block, maybe_keys) = verifier.verify(block_origin, header, justifications, block.body)
 		.map_err(|msg| {
 			if let Some(ref peer) = peer {
 				trace!(target: "sync", "Verifying {}({}) from {} failed: {}", number, hash, peer, msg);

substrate/primitives/consensus/common/src/import_queue/basic_queue.rs

@@ -18,7 +18,7 @@
 use std::{pin::Pin, time::Duration, marker::PhantomData};
 use futures::{prelude::*, task::Context, task::Poll};
 use futures_timer::Delay;
-use sp_runtime::{Justification, traits::{Block as BlockT, Header as HeaderT, NumberFor}};
+use sp_runtime::{Justification, Justifications, traits::{Block as BlockT, Header as HeaderT, NumberFor}};
 use sp_utils::mpsc::{TracingUnboundedSender, tracing_unbounded, TracingUnboundedReceiver};
 use prometheus_endpoint::Registry;
 
@@ -112,22 +112,24 @@ impl<B: BlockT, Transaction: Send> ImportQueue<B> for BasicQueue<B, Transaction>
 		}
 	}
 
-	fn import_justification(
+	fn import_justifications(
 		&mut self,
 		who: Origin,
 		hash: B::Hash,
 		number: NumberFor<B>,
-		justification: Justification,
+		justifications: Justifications,
 	) {
-		let res = self.justification_sender.unbounded_send(
+		for justification in justifications {
-			worker_messages::ImportJustification(who, hash, number, justification),
+			let res = self.justification_sender.unbounded_send(
-		);
+				worker_messages::ImportJustification(who, hash, number, justification),
-
-		if res.is_err() {
-			log::error!(
-				target: "sync",
-				"import_justification: Background import task is no longer alive"
 			);
+
+			if res.is_err() {
+				log::error!(
+					target: "sync",
+					"import_justification: Background import task is no longer alive"
+				);
+			}
 		}
 	}
 
@@ -281,7 +283,7 @@ impl<B: BlockT> BlockImportWorker<B> {
 		who: Origin,
 		hash: B::Hash,
 		number: NumberFor<B>,
-		justification: Justification
+		justification: Justification,
 	) {
 		let started = wasm_timer::Instant::now();
 		let success = self.justification_import.as_mut().map(|justification_import| {
@@ -442,7 +444,7 @@ mod tests {
 			&mut self,
 			origin: BlockOrigin,
 			header: Header,
-			_justification: Option<Justification>,
+			_justifications: Option<Justifications>,
 			_body: Option<Vec<Extrinsic>>,
 		) -> Result<(BlockImportParams<Block, ()>, Option<Vec<(CacheKeyId, Vec<u8>)>>), String> {
 			Ok((BlockImportParams::new(origin, header), None))
@@ -541,7 +543,7 @@ mod tests {
 					hash,
 					header: Some(header),
 					body: None,
-					justification: None,
+					justifications: None,
 					origin: None,
 					allow_missing_state: false,
 					import_existing: false,
@@ -554,12 +556,11 @@ mod tests {
 
 		let mut import_justification = || {
 			let hash = Hash::random();
-
 			block_on(finality_sender.send(worker_messages::ImportJustification(
 				libp2p::PeerId::random(),
 				hash,
 				1,
-				Vec::new(),
+				(*b"TEST", Vec::new()),
 			)))
 			.unwrap();
 

substrate/primitives/runtime/src/generic/block.rs

@@ -30,7 +30,7 @@ use crate::traits::{
 	self, Member, Block as BlockT, Header as HeaderT, MaybeSerialize, MaybeMallocSizeOf,
 	NumberFor,
 };
-use crate::Justification;
+use crate::Justifications;
 
 /// Something to identify a block.
 #[derive(PartialEq, Eq, Clone, RuntimeDebug)]
@@ -112,5 +112,5 @@ pub struct SignedBlock<Block> {
 	/// Full block.
 	pub block: Block,
 	/// Block justification.
-	pub justification: Option<Justification>,
+	pub justifications: Option<Justifications>,
 }

substrate/primitives/runtime/src/lib.rs

@@ -96,7 +96,65 @@ pub use either::Either;
 /// the block itself would allow swapping justifications to change the block's hash
 /// (and thus fork the chain). Sending a `Justification` alongside a block instead
 /// bypasses this problem.
-pub type Justification = Vec<u8>;
+///
+/// Each justification is provided as an encoded blob, and is tagged with an ID
+/// to identify the consensus engine that generated the proof (we might have
+/// multiple justifications from different engines for the same block).
+pub type Justification = (ConsensusEngineId, EncodedJustification);
+
+/// The encoded justification specific to a consensus engine.
+pub type EncodedJustification = Vec<u8>;
+
+/// Collection of justifications for a given block, multiple justifications may
+/// be provided by different consensus engines for the same block.
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+#[derive(Debug, Clone, PartialEq, Eq, Encode, Decode)]
+pub struct Justifications(Vec<Justification>);
+
+impl Justifications {
+	/// Return an iterator over the justifications.
+	pub fn iter(&self) -> impl Iterator<Item = &Justification> {
+		self.0.iter()
+	}
+
+	/// Append a justification. Returns false if a justification with the same
+	/// `ConsensusEngineId` already exists, in which case the justification is
+	/// not inserted.
+	pub fn append(&mut self, justification: Justification) -> bool {
+		if self.get(justification.0).is_some() {
+			return false;
+		}
+		self.0.push(justification);
+		true
+	}
+
+	/// Return the encoded justification for the given consensus engine, if it
+	/// exists.
+	pub fn get(&self, engine_id: ConsensusEngineId) -> Option<&EncodedJustification> {
+		self.iter().find(|j| j.0 == engine_id).map(|j| &j.1)
+	}
+
+	/// Return a copy of the encoded justification for the given consensus
+	/// engine, if it exists.
+	pub fn into_justification(self, engine_id: ConsensusEngineId) -> Option<EncodedJustification> {
+		self.into_iter().find(|j| j.0 == engine_id).map(|j| j.1)
+	}
+}
+
+impl IntoIterator for Justifications {
+	type Item = Justification;
+	type IntoIter = sp_std::vec::IntoIter<Self::Item>;
+
+	fn into_iter(self) -> Self::IntoIter {
+		self.0.into_iter()
+	}
+}
+
+impl From<Justification> for Justifications {
+	fn from(justification: Justification) -> Self {
+		Self(vec![justification])
+	}
+}
 
 use traits::{Verify, Lazy};
 

substrate/test-utils/client/src/client_ext.rs

@@ -24,7 +24,7 @@ use sp_consensus::{
 	BlockImportParams, BlockImport, BlockOrigin, Error as ConsensusError,
 	ForkChoiceStrategy,
 };
-use sp_runtime::Justification;
+use sp_runtime::{Justification, Justifications};
 use sp_runtime::traits::{Block as BlockT};
 use sp_runtime::generic::BlockId;
 use codec::alloc::collections::hash_map::HashMap;
@@ -51,15 +51,14 @@ pub trait ClientBlockImportExt<Block: BlockT>: Sized {
 	fn import_as_best(&mut self, origin: BlockOrigin, block: Block) -> Result<(), ConsensusError>;
 
 	/// Import a block and finalize it.
-	fn import_as_final(&mut self, origin: BlockOrigin, block: Block)
+	fn import_as_final(&mut self, origin: BlockOrigin, block: Block) -> Result<(), ConsensusError>;
-		-> Result<(), ConsensusError>;
 
-	/// Import block with justification, finalizes block.
+	/// Import block with justification(s), finalizes block.
 	fn import_justified(
 		&mut self,
 		origin: BlockOrigin,
 		block: Block,
-		justification: Justification
+		justifications: Justifications,
 	) -> Result<(), ConsensusError>;
 }
 
@@ -119,11 +118,11 @@ impl<Block: BlockT, T, Transaction> ClientBlockImportExt<Block> for std::sync::A
 		&mut self,
 		origin: BlockOrigin,
 		block: Block,
-		justification: Justification,
+		justifications: Justifications,
 	) -> Result<(), ConsensusError> {
 		let (header, extrinsics) = block.deconstruct();
 		let mut import = BlockImportParams::new(origin, header);
-		import.justification = Some(justification);
+		import.justifications = Some(justifications);
 		import.body = Some(extrinsics);
 		import.finalized = true;
 		import.fork_choice = Some(ForkChoiceStrategy::LongestChain);
@@ -168,11 +167,11 @@ impl<B, E, RA, Block: BlockT> ClientBlockImportExt<Block> for Client<B, E, Block
 		&mut self,
 		origin: BlockOrigin,
 		block: Block,
-		justification: Justification,
+		justifications: Justifications,
 	) -> Result<(), ConsensusError> {
 		let (header, extrinsics) = block.deconstruct();
 		let mut import = BlockImportParams::new(origin, header);
-		import.justification = Some(justification);
+		import.justifications = Some(justifications);
 		import.body = Some(extrinsics);
 		import.finalized = true;
 		import.fork_choice = Some(ForkChoiceStrategy::LongestChain);