Allow import withouth state verification (#4031)

* Allow import without state verification

* Explicit None

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

substrate/core/client/db/src/lib.rs

@@ -457,6 +457,7 @@ pub struct BlockImportOperation<Block: BlockT, H: Hasher> {
 	aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	finalized_blocks: Vec<(BlockId<Block>, Option<Justification>)>,
 	set_head: Option<BlockId<Block>>,
+	commit_state: bool,
 }
 
 impl<Block: BlockT, H: Hasher> BlockImportOperation<Block, H> {
@@ -531,6 +532,7 @@ impl<Block> client::backend::BlockImportOperation<Block, Blake2Hasher>
 		);
 
 		self.db_updates = transaction;
+		self.commit_state = true;
 		Ok(root)
 	}
 
@@ -783,6 +785,7 @@ pub struct Backend<Block: BlockT> {
 	canonicalization_delay: u64,
 	shared_cache: SharedCache<Block, Blake2Hasher>,
 	import_lock: Mutex<()>,
+	is_archive: bool,
 }
 
 impl<Block: BlockT<Hash=H256>> Backend<Block> {
@@ -843,6 +846,7 @@ impl<Block: BlockT<Hash=H256>> Backend<Block> {
 				config.state_cache_child_ratio.unwrap_or(DEFAULT_CHILD_RATIO),
 			),
 			import_lock: Default::default(),
+			is_archive: is_archive_pruning,
 		})
 	}
 
@@ -894,6 +898,12 @@ impl<Block: BlockT<Hash=H256>> Backend<Block> {
 		inmem
 	}
 
+	/// Returns total numbet of blocks (headers) in the block DB.
+	#[cfg(feature = "test-helpers")]
+	pub fn blocks_count(&self) -> u64 {
+		self.blockchain.db.iter(columns::HEADER).count() as u64
+	}
+
 	/// Read (from storage or cache) changes trie config.
 	///
 	/// Currently changes tries configuration is set up once (at genesis) and could not
@@ -1115,7 +1125,7 @@ impl<Block: BlockT<Hash=H256>> Backend<Block> {
 			);
 
 			transaction.put(columns::HEADER, &lookup_key, &pending_block.header.encode());
-			if let Some(body) = pending_block.body {
+			if let Some(body) = &pending_block.body {
 				transaction.put(columns::BODY, &lookup_key, &body.encode());
 			}
 			if let Some(justification) = pending_block.justification {
@@ -1127,21 +1137,26 @@ impl<Block: BlockT<Hash=H256>> Backend<Block> {
 				transaction.put(columns::META, meta_keys::GENESIS_HASH, hash.as_ref());
 			}
 
-			let mut changeset: state_db::ChangeSet<Vec<u8>> = state_db::ChangeSet::default();
-			for (key, (val, rc)) in operation.db_updates.drain() {
-				if rc > 0 {
-					changeset.inserted.push((key, val.to_vec()));
-				} else if rc < 0 {
-					changeset.deleted.push(key);
+			let finalized = if operation.commit_state {
+				let mut changeset: state_db::ChangeSet<Vec<u8>> = state_db::ChangeSet::default();
+				for (key, (val, rc)) in operation.db_updates.drain() {
+					if rc > 0 {
+						changeset.inserted.push((key, val.to_vec()));
+					} else if rc < 0 {
+						changeset.deleted.push(key);
+					}
 				}
-			}
-			let number_u64 = number.saturated_into::<u64>();
-			let commit = self.storage.state_db.insert_block(&hash, number_u64, &pending_block.header.parent_hash(), changeset)
-				.map_err(|e: state_db::Error<io::Error>| client::error::Error::from(format!("State database error: {:?}", e)))?;
-			apply_state_commit(&mut transaction, commit);
+				let number_u64 = number.saturated_into::<u64>();
+				let commit = self.storage.state_db.insert_block(&hash, number_u64, &pending_block.header.parent_hash(), changeset)
+					.map_err(|e: state_db::Error<io::Error>| client::error::Error::from(format!("State database error: {:?}", e)))?;
+				apply_state_commit(&mut transaction, commit);
 
-			// Check if need to finalize. Genesis is always finalized instantly.
-			let finalized = number_u64 == 0 || pending_block.leaf_state.is_final();
+				// Check if need to finalize. Genesis is always finalized instantly.
+				let finalized = number_u64 == 0 || pending_block.leaf_state.is_final();
+				finalized
+			} else {
+				false
+			};
 
 			let header = &pending_block.header;
 			let is_best = pending_block.leaf_state.is_best();
@@ -1347,6 +1362,7 @@ impl<Block> client::backend::Backend<Block, Blake2Hasher> for Backend<Block> whe
 			aux_ops: Vec::new(),
 			finalized_blocks: Vec::new(),
 			set_head: None,
+			commit_state: false,
 		})
 	}
 
@@ -1356,6 +1372,7 @@ impl<Block> client::backend::Backend<Block, Blake2Hasher> for Backend<Block> whe
 		block: BlockId<Block>,
 	) -> ClientResult<()> {
 		operation.old_state = self.state_at(block)?;
+		operation.commit_state = true;
 		Ok(())
 	}
 
@@ -1478,6 +1495,9 @@ impl<Block> client::backend::Backend<Block, Blake2Hasher> for Backend<Block> whe
 		match self.blockchain.header(block) {
 			Ok(Some(ref hdr)) => {
 				let hash = hdr.hash();
+				if !self.have_state_at(&hash, *hdr.number()) {
+					return Err(client::error::Error::UnknownBlock(format!("State already discarded for {:?}", block)))
+				}
 				if let Ok(()) = self.storage.state_db.pin(&hash) {
 					let root = H256::from_slice(hdr.state_root().as_ref());
 					let db_state = DbState::new(self.storage.clone(), root);
@@ -1493,7 +1513,16 @@ impl<Block> client::backend::Backend<Block, Blake2Hasher> for Backend<Block> whe
 	}
 
 	fn have_state_at(&self, hash: &Block::Hash, number: NumberFor<Block>) -> bool {
-		!self.storage.state_db.is_pruned(hash, number.saturated_into::<u64>())
+		if self.is_archive {
+			match self.blockchain.header(BlockId::Hash(hash.clone())) {
+				Ok(Some(header)) => {
+					state_machine::Storage::get(self.storage.as_ref(), &header.state_root(), (&[], None)).unwrap_or(None).is_some()
+				},
+				_ => false,
+			}
+		} else {
+			!self.storage.state_db.is_pruned(hash, number.saturated_into::<u64>())
+		}
 	}
 
 	fn destroy_state(&self, state: Self::State) -> ClientResult<()> {
@@ -1581,7 +1610,7 @@ mod tests {
 		};
 		let mut op = backend.begin_operation().unwrap();
 		backend.begin_state_operation(&mut op, block_id).unwrap();
-		op.set_block_data(header, None, None, NewBlockState::Best).unwrap();
+		op.set_block_data(header, Some(Vec::new()), None, NewBlockState::Best).unwrap();
 		op.update_changes_trie((changes_trie_update, ChangesTrieCacheAction::Clear)).unwrap();
 		backend.commit_operation(op).unwrap();
 

substrate/core/client/src/client.rs

@@ -838,15 +838,22 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			finalized,
 			auxiliary,
 			fork_choice,
+			allow_missing_state,
 		} = import_block;
 
 		assert!(justification.is_some() && finalized || justification.is_none());
 
 		let parent_hash = header.parent_hash().clone();
+		let mut enact_state = true;
 
-		match self.backend.blockchain().status(BlockId::Hash(parent_hash))? {
-			blockchain::BlockStatus::InChain => {},
-			blockchain::BlockStatus::Unknown => return Ok(ImportResult::UnknownParent),
+		match self.block_status(&BlockId::Hash(parent_hash))? {
+			BlockStatus::Unknown => return Ok(ImportResult::UnknownParent),
+			BlockStatus::InChainWithState | BlockStatus::Queued => {},
+			BlockStatus::InChainPruned if allow_missing_state => {
+				enact_state = false;
+			},
+			BlockStatus::InChainPruned => return Ok(ImportResult::MissingState),
+			BlockStatus::KnownBad => return Ok(ImportResult::KnownBad),
 		}
 
 		let import_headers = if post_digests.is_empty() {
@@ -875,6 +882,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			finalized,
 			auxiliary,
 			fork_choice,
+			enact_state,
 		);
 
 		if let Ok(ImportResult::Imported(ref aux)) = result {
@@ -902,6 +910,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		finalized: bool,
 		aux: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 		fork_choice: ForkChoiceStrategy,
+		enact_state: bool,
 	) -> error::Result<ImportResult> where
 		E: CallExecutor<Block, Blake2Hasher> + Send + Sync + Clone,
 	{
@@ -927,22 +936,39 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			BlockOrigin::Genesis | BlockOrigin::NetworkInitialSync | BlockOrigin::File => false,
 		};
 
-		self.backend.begin_state_operation(&mut operation.op, BlockId::Hash(parent_hash))?;
+		let storage_changes = match &body {
+			Some(body) if enact_state => {
+				self.backend.begin_state_operation(&mut operation.op, BlockId::Hash(parent_hash))?;
 
-		// ensure parent block is finalized to maintain invariant that
-		// finality is called sequentially.
-		if finalized {
-			self.apply_finality_with_block_hash(operation, parent_hash, None, info.best_hash, make_notifications)?;
-		}
+				// ensure parent block is finalized to maintain invariant that
+				// finality is called sequentially.
+				if finalized {
+					self.apply_finality_with_block_hash(operation, parent_hash, None, info.best_hash, make_notifications)?;
+				}
 
-		// FIXME #1232: correct path logic for when to execute this function
-		let (storage_update, changes_update, storage_changes) = self.block_execution(
-			&operation.op,
-			&import_headers,
-			origin,
-			hash,
-			body.clone(),
-		)?;
+				// FIXME #1232: correct path logic for when to execute this function
+				let (storage_update, changes_update, storage_changes) = self.block_execution(
+					&operation.op,
+					&import_headers,
+					origin,
+					hash,
+					&body,
+				)?;
+
+				operation.op.update_cache(new_cache);
+				if let Some(storage_update) = storage_update {
+					operation.op.update_db_storage(storage_update)?;
+				}
+				if let Some(storage_changes) = storage_changes.clone() {
+					operation.op.update_storage(storage_changes.0, storage_changes.1)?;
+				}
+				if let Some(Some(changes_update)) = changes_update {
+					operation.op.update_changes_trie(changes_update)?;
+				}
+				storage_changes
+			},
+			_ => None,
+		};
 
 		let is_new_best = finalized || match fork_choice {
 			ForkChoiceStrategy::LongestChain => import_headers.post().number() > &info.best_number,
@@ -977,17 +1003,6 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			leaf_state,
 		)?;
 
-		operation.op.update_cache(new_cache);
-		if let Some(storage_update) = storage_update {
-			operation.op.update_db_storage(storage_update)?;
-		}
-		if let Some(storage_changes) = storage_changes.clone() {
-			operation.op.update_storage(storage_changes.0, storage_changes.1)?;
-		}
-		if let Some(Some(changes_update)) = changes_update {
-			operation.op.update_changes_trie(changes_update)?;
-		}
-
 		operation.op.insert_aux(aux)?;
 
 		if make_notifications {
@@ -1014,7 +1029,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		import_headers: &PrePostHeader<Block::Header>,
 		origin: BlockOrigin,
 		hash: Block::Hash,
-		body: Option<Vec<Block::Extrinsic>>,
+		body: &[Block::Extrinsic],
 	) -> error::Result<(
 		Option<StorageUpdate<B, Block>>,
 		Option<Option<ChangesUpdate<Block>>>,
@@ -1052,7 +1067,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 
 				let encoded_block = <Block as BlockT>::encode_from(
 					import_headers.pre(),
-					&body.unwrap_or_default()
+					body,
 				);
 
 				let (_, storage_update, changes_update) = self.executor
@@ -1523,7 +1538,7 @@ impl<'a, B, E, Block, RA> consensus::BlockImport<Block> for &'a Client<B, E, Blo
 		&mut self,
 		block: BlockCheckParams<Block>,
 	) -> Result<ImportResult, Self::Error> {
-		let BlockCheckParams { hash, number, parent_hash } = block;
+		let BlockCheckParams { hash, number, parent_hash, allow_missing_state } = block;
 
 		if let Some(h) = self.fork_blocks.as_ref().and_then(|x| x.get(&number)) {
 			if &hash != h  {
@@ -1541,7 +1556,9 @@ impl<'a, B, E, Block, RA> consensus::BlockImport<Block> for &'a Client<B, E, Blo
 			.map_err(|e| ConsensusError::ClientImport(e.to_string()))?
 		{
 			BlockStatus::InChainWithState | BlockStatus::Queued => {},
-			BlockStatus::Unknown | BlockStatus::InChainPruned => return Ok(ImportResult::UnknownParent),
+			BlockStatus::Unknown => return Ok(ImportResult::UnknownParent),
+			BlockStatus::InChainPruned if allow_missing_state => {},
+			BlockStatus::InChainPruned => return Ok(ImportResult::MissingState),
 			BlockStatus::KnownBad => return Ok(ImportResult::KnownBad),
 		}
 
@@ -1553,7 +1570,6 @@ impl<'a, B, E, Block, RA> consensus::BlockImport<Block> for &'a Client<B, E, Blo
 			BlockStatus::KnownBad => return Ok(ImportResult::KnownBad),
 		}
 
-
 		Ok(ImportResult::imported(false))
 	}
 }

substrate/core/consensus/aura/src/lib.rs

@@ -267,6 +267,7 @@ impl<H, B, C, E, I, P, Error, SO> slots::SimpleSlotWorker<B> for AuraWorker<C, E
 				finalized: false,
 				auxiliary: Vec::new(),
 				fork_choice: ForkChoiceStrategy::LongestChain,
+				allow_missing_state: false,
 			}
 		})
 	}
@@ -570,6 +571,7 @@ impl<B: BlockT, C, P, T> Verifier<B> for AuraVerifier<C, P, T> where
 					justification,
 					auxiliary: Vec::new(),
 					fork_choice: ForkChoiceStrategy::LongestChain,
+					allow_missing_state: false,
 				};
 
 				Ok((block_import_params, maybe_keys))

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

@@ -430,6 +430,7 @@ impl<B, C, E, I, Error, SO> slots::SimpleSlotWorker<B> for BabeWorker<B, C, E, I
 				// option to specify one.
 				// https://github.com/paritytech/substrate/issues/3623
 				fork_choice: ForkChoiceStrategy::LongestChain,
+				allow_missing_state: false,
 			}
 		})
 	}
@@ -741,6 +742,7 @@ impl<B, E, Block, RA, PRA> Verifier<Block> for BabeVerifier<B, E, Block, RA, PRA
 					// option to specify one.
 					// https://github.com/paritytech/substrate/issues/3623
 					fork_choice: ForkChoiceStrategy::LongestChain,
+					allow_missing_state: false,
 				};
 
 				Ok((block_import_params, Default::default()))

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

@@ -578,6 +578,7 @@ fn propose_and_import_block(
 			finalized: false,
 			auxiliary: Vec::new(),
 			fork_choice: ForkChoiceStrategy::LongestChain,
+			allow_missing_state: false,
 		},
 		Default::default(),
 	).unwrap();

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

@@ -35,11 +35,15 @@ pub enum ImportResult {
 	KnownBad,
 	/// Block parent is not in the chain.
 	UnknownParent,
+	/// Parent state is missing.
+	MissingState,
 }
 
 /// Auxiliary data associated with an imported block result.
 #[derive(Debug, Default, PartialEq, Eq)]
 pub struct ImportedAux {
+	/// Only the header has been imported. Block body verification was skipped.
+	pub header_only: bool,
 	/// Clear all pending justification requests.
 	pub clear_justification_requests: bool,
 	/// Request a justification for the given block.
@@ -98,6 +102,8 @@ pub struct BlockCheckParams<Block: BlockT> {
 	pub number: NumberFor<Block>,
 	/// Parent hash of the block that we verify.
 	pub parent_hash: Block::Hash,
+	/// Allow importing the block skipping state verification if parent state is missing.
+	pub allow_missing_state: bool,
 }
 
 /// Data required to import a Block.
@@ -133,6 +139,8 @@ pub struct BlockImportParams<Block: BlockT> {
 	/// Fork choice strategy of this import. This should only be set by a
 	/// synchronous import, otherwise it may race against other imports.
 	pub fork_choice: ForkChoiceStrategy,
+	/// Allow importing the block skipping state verification if parent state is missing.
+	pub allow_missing_state: bool,
 }
 
 impl<Block: BlockT> BlockImportParams<Block> {

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

@@ -63,6 +63,8 @@ pub struct IncomingBlock<B: BlockT> {
 	pub justification: Option<Justification>,
 	/// The peer, we received this from
 	pub origin: Option<Origin>,
+	/// Allow importing the block skipping state verification if parent state is missing.
+	pub allow_missing_state: bool,
 }
 
 /// Type of keys in the blockchain cache that consensus module could use for its needs.
@@ -203,6 +205,10 @@ pub fn import_single_block<B: BlockT, V: Verifier<B>>(
 				Ok(BlockImportResult::ImportedKnown(number))
 			},
 			Ok(ImportResult::Imported(aux)) => Ok(BlockImportResult::ImportedUnknown(number, aux, peer.clone())),
+			Ok(ImportResult::MissingState) => {
+				debug!(target: "sync", "Parent state is missing for {}: {:?}, parent: {:?}", number, hash, parent_hash);
+				Err(BlockImportError::UnknownParent)
+			},
 			Ok(ImportResult::UnknownParent) => {
 				debug!(target: "sync", "Block with unknown parent {}: {:?}, parent: {:?}", number, hash, parent_hash);
 				Err(BlockImportError::UnknownParent)
@@ -217,12 +223,17 @@ pub fn import_single_block<B: BlockT, V: Verifier<B>>(
 			}
 		}
 	};
-	match import_error(import_handle.check_block(BlockCheckParams { hash, number, parent_hash }))? {
+	match import_error(import_handle.check_block(BlockCheckParams {
+		hash,
+		number,
+		parent_hash,
+		allow_missing_state: block.allow_missing_state,
+	}))? {
 		BlockImportResult::ImportedUnknown { .. } => (),
 		r => return Ok(r), // Any other successful result means that the block is already imported.
 	}
 
-	let (import_block, maybe_keys) = verifier.verify(block_origin, header, justification, block.body)
+	let (mut import_block, maybe_keys) = verifier.verify(block_origin, header, justification, block.body)
 		.map_err(|msg| {
 			if let Some(ref peer) = peer {
 				trace!(target: "sync", "Verifying {}({}) from {} failed: {}", number, hash, peer, msg);
@@ -236,6 +247,7 @@ pub fn import_single_block<B: BlockT, V: Verifier<B>>(
 	if let Some(keys) = maybe_keys {
 		cache.extend(keys.into_iter());
 	}
+	import_block.allow_missing_state = block.allow_missing_state;
 
 	import_error(import_handle.import_block(import_block, cache))
 }

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

@@ -304,6 +304,7 @@ impl<B: BlockT<Hash=H256>, C, S, Algorithm> Verifier<B> for PowVerifier<B, C, S,
 			justification,
 			auxiliary: vec![(key, Some(aux.encode()))],
 			fork_choice: ForkChoiceStrategy::Custom(aux.total_difficulty > best_aux.total_difficulty),
+			allow_missing_state: false,
 		};
 
 		Ok((import_block, None))
@@ -531,6 +532,7 @@ fn mine_loop<B: BlockT<Hash=H256>, C, Algorithm, E, SO, S>(
 			finalized: false,
 			auxiliary: vec![(key, Some(aux.encode()))],
 			fork_choice: ForkChoiceStrategy::Custom(true),
+			allow_missing_state: false,
 		};
 
 		block_import.import_block(import_block, HashMap::default())

substrate/core/finality-grandpa/src/light_import.rs

@@ -663,6 +663,7 @@ pub mod tests {
 			finalized: false,
 			auxiliary: Vec::new(),
 			fork_choice: ForkChoiceStrategy::LongestChain,
+			allow_missing_state: true,
 		};
 		do_import_block::<_, _, _, TestJustification>(
 			&client,
@@ -680,6 +681,7 @@ pub mod tests {
 			bad_justification: false,
 			needs_finality_proof: false,
 			is_new_best: true,
+			header_only: false,
 		}));
 	}
 
@@ -692,6 +694,7 @@ pub mod tests {
 			bad_justification: false,
 			needs_finality_proof: false,
 			is_new_best: true,
+			header_only: false,
 		}));
 	}
 
@@ -705,6 +708,7 @@ pub mod tests {
 			bad_justification: false,
 			needs_finality_proof: true,
 			is_new_best: true,
+			header_only: false,
 		}));
 	}
 
@@ -721,6 +725,7 @@ pub mod tests {
 				bad_justification: false,
 				needs_finality_proof: true,
 				is_new_best: false,
+				header_only: false,
 			},
 		));
 	}

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

@@ -974,6 +974,7 @@ fn allows_reimporting_change_blocks() {
 			finalized: false,
 			auxiliary: Vec::new(),
 			fork_choice: ForkChoiceStrategy::LongestChain,
+			allow_missing_state: false,
 		}
 	};
 
@@ -985,6 +986,7 @@ fn allows_reimporting_change_blocks() {
 			bad_justification: false,
 			needs_finality_proof: false,
 			is_new_best: true,
+			header_only: false,
 		}),
 	);
 
@@ -1025,6 +1027,7 @@ fn test_bad_justification() {
 			finalized: false,
 			auxiliary: Vec::new(),
 			fork_choice: ForkChoiceStrategy::LongestChain,
+			allow_missing_state: false,
 		}
 	};
 
@@ -1721,6 +1724,7 @@ fn imports_justification_for_regular_blocks_on_import() {
 		finalized: false,
 		auxiliary: Vec::new(),
 		fork_choice: ForkChoiceStrategy::LongestChain,
+		allow_missing_state: false,
 	};
 
 	assert_eq!(

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

@@ -480,13 +480,7 @@ impl<B: BlockT> ChainSync<B> {
 			return;
 		}
 
-		let block_status = self.client.block_status(&BlockId::Number(number - One::one()))
-			.unwrap_or(BlockStatus::Unknown);
-		if block_status == BlockStatus::InChainPruned {
-			trace!(target: "sync", "Refusing to sync ancient block {:?}", hash);
-			return;
-		}
-
+		trace!(target: "sync", "Downloading requested old fork {:?}", hash);
 		self.is_idle = false;
 		for peer_id in &peers {
 			if let Some(peer) = self.peers.get_mut(peer_id) {
@@ -571,7 +565,7 @@ impl<B: BlockT> ChainSync<B> {
 		let major_sync = self.status().state == SyncState::Downloading;
 		let blocks = &mut self.blocks;
 		let attrs = &self.required_block_attributes;
-		let fork_targets = &self.fork_targets;
+		let fork_targets = &mut self.fork_targets;
 		let mut have_requests = false;
 		let last_finalized = self.client.info().chain.finalized_number;
 		let best_queued = self.best_queued_number;
@@ -646,6 +640,7 @@ impl<B: BlockT> ChainSync<B> {
 									body: block_data.block.body,
 									justification: block_data.block.justification,
 									origin: block_data.origin,
+									allow_missing_state: false,
 								}
 							}).collect()
 					}
@@ -658,14 +653,15 @@ impl<B: BlockT> ChainSync<B> {
 								body: b.body,
 								justification: b.justification,
 								origin: Some(who.clone()),
+								allow_missing_state: true,
 							}
 						}).collect()
 					}
 					PeerSyncState::AncestorSearch(num, state) => {
-						let block_hash_match = match (blocks.get(0), self.client.block_hash(*num)) {
+						let matching_hash = match (blocks.get(0), self.client.block_hash(*num)) {
 							(Some(block), Ok(maybe_our_block_hash)) => {
 								trace!(target: "sync", "Got ancestry block #{} ({}) from peer {}", num, block.hash, who);
-								maybe_our_block_hash.map_or(false, |x| x == block.hash)
+								maybe_our_block_hash.filter(|x| x == &block.hash)
 							},
 							(None, _) => {
 								debug!(target: "sync", "Invalid response when searching for ancestor from {}", who);
@@ -676,27 +672,34 @@ impl<B: BlockT> ChainSync<B> {
 								return Err(BadPeer(who, ANCESTRY_BLOCK_ERROR_REPUTATION_CHANGE))
 							}
 						};
-						if block_hash_match && peer.common_number < *num {
+						if matching_hash.is_some() && peer.common_number < *num {
 							peer.common_number = *num;
 						}
-						if !block_hash_match && num.is_zero() {
+						if matching_hash.is_none() && num.is_zero() {
 							trace!(target:"sync", "Ancestry search: genesis mismatch for peer {}", who);
 							return Err(BadPeer(who, GENESIS_MISMATCH_REPUTATION_CHANGE))
 						}
-						if let Some((next_state, next_num)) = handle_ancestor_search_state(state, *num, block_hash_match) {
+						if let Some((next_state, next_num)) = handle_ancestor_search_state(state, *num, matching_hash.is_some()) {
 							peer.state = PeerSyncState::AncestorSearch(next_num, next_state);
 							return Ok(OnBlockData::Request(who, ancestry_request::<B>(next_num)))
 						} else {
 							// Ancestry search is complete. Check if peer is on a stale fork unknown to us and
 							// add it to sync targets if necessary.
-							trace!(target: "sync", "Ancestry search complete. Ours={} ({}), Theirs={} ({}), Common={}",
+							trace!(target: "sync", "Ancestry search complete. Ours={} ({}), Theirs={} ({}), Common={:?} ({})",
 								self.best_queued_hash,
 								self.best_queued_number,
 								peer.best_hash,
 								peer.best_number,
-								peer.common_number
+								matching_hash,
+								peer.common_number,
 							);
-							if peer.common_number < peer.best_number && peer.best_number < self.best_queued_number {
+							let client = &self.client;
+							if peer.common_number < peer.best_number
+								&& peer.best_number < self.best_queued_number
+								&& matching_hash.and_then(
+									|h| client.block_status(&BlockId::Hash(h)).ok()
+								).unwrap_or(BlockStatus::Unknown) != BlockStatus::InChainPruned
+							{
 								trace!(target: "sync", "Added fork target {} for {}" , peer.best_hash, who);
 								self.fork_targets
 									.entry(peer.best_hash.clone())
@@ -1250,25 +1253,31 @@ fn peer_block_request<B: BlockT>(
 /// Get pending fork sync targets for a peer.
 fn fork_sync_request<B: BlockT>(
 	id: &PeerId,
-	targets: &HashMap<B::Hash, ForkTarget<B>>,
+	targets: &mut HashMap<B::Hash, ForkTarget<B>>,
 	best_num: NumberFor<B>,
 	finalized: NumberFor<B>,
 	attributes: &message::BlockAttributes,
 	check_block: impl Fn(&B::Hash) -> BlockStatus,
 ) -> Option<(B::Hash, BlockRequest<B>)>
 {
+	targets.retain(|hash, r| if r.number > finalized {
+		true
+	} else {
+		trace!(target: "sync", "Removed expired fork sync request {:?} (#{})", hash, r.number);
+		false
+	});
 	for (hash, r) in targets {
 		if !r.peers.contains(id) {
 			continue
 		}
 		if r.number <= best_num {
-			trace!(target: "sync", "Downloading requested fork {:?} from {}", hash, id);
 			let parent_status = r.parent_hash.as_ref().map_or(BlockStatus::Unknown, check_block);
 			let mut count = (r.number - finalized).saturated_into::<u32>(); // up to the last finalized block
 			if parent_status != BlockStatus::Unknown {
 				// request only single block
 				count = 1;
 			}
+			trace!(target: "sync", "Downloading requested fork {:?} from {}, {} blocks", hash, id, count);
 			return Some((hash.clone(), message::generic::BlockRequest {
 				id: 0,
 				fields: attributes.clone(),

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

@@ -37,9 +37,10 @@ fn prepare_good_block() -> (TestClient, Hash, u64, PeerId, IncomingBlock<Block>)
 	(client, hash, number, peer_id.clone(), IncomingBlock {
 		hash,
 		header,
-		body: None,
+		body: Some(Vec::new()),
 		justification,
-		origin: Some(peer_id.clone())
+		origin: Some(peer_id.clone()),
+		allow_missing_state: false,
 	})
 }
 
@@ -53,7 +54,7 @@ fn import_single_good_block_works() {
 	match import_single_block(&mut test_client::new(), BlockOrigin::File, block, &mut PassThroughVerifier(true)) {
 		Ok(BlockImportResult::ImportedUnknown(ref num, ref aux, ref org))
 			if *num == number && *aux == expected_aux && *org == Some(peer_id) => {}
-		_ => panic!()
+		r @ _ => panic!("{:?}", r)
 	}
 }
 

substrate/core/network/src/test/mod.rs

@@ -96,6 +96,7 @@ impl<B: BlockT> Verifier<B> for PassThroughVerifier {
 			post_digests: vec![],
 			auxiliary: Vec::new(),
 			fork_choice: ForkChoiceStrategy::LongestChain,
+			allow_missing_state: false,
 		}, maybe_keys))
 	}
 }
@@ -374,16 +375,10 @@ impl<D, S: NetworkSpecialization<Block>> Peer<D, S> {
 		}
 	}
 
-	/// Count the current number of known blocks. Note that:
-	///  1. this might be expensive as it creates an in-memory-copy of the chain
-	///     to count the blocks, thus if you have a different way of testing this
-	///     (e.g. `info.best_hash`) - use that.
-	///  2. This is not always increasing nor accurate, as the
-	///     orphaned and proven-to-never-finalized blocks may be pruned at any time.
-	///     Therefore, this number can drop again.
-	pub fn blocks_count(&self) -> usize {
+	/// Count the total number of imported blocks.
+	pub fn blocks_count(&self) -> u64 {
 		self.backend.as_ref().map(
-			|backend| backend.as_in_memory().blockchain().blocks_count()
+			|backend| backend.blocks_count()
 		).unwrap_or(0)
 	}
 }
@@ -526,9 +521,16 @@ pub trait TestNetFactory: Sized {
 		net
 	}
 
-	/// Add a full peer.
 	fn add_full_peer(&mut self, config: &ProtocolConfig) {
-		let test_client_builder = TestClientBuilder::with_default_backend();
+		self.add_full_peer_with_states(config, None)
+	}
+
+	/// Add a full peer.
+	fn add_full_peer_with_states(&mut self, config: &ProtocolConfig, keep_blocks: Option<u32>) {
+		let test_client_builder = match keep_blocks {
+			Some(keep_blocks) => TestClientBuilder::with_pruning_window(keep_blocks),
+			None => TestClientBuilder::with_default_backend(),
+		};
 		let backend = test_client_builder.backend();
 		let (c, longest_chain) = test_client_builder.build_with_longest_chain();
 		let client = Arc::new(c);
@@ -686,7 +688,7 @@ pub trait TestNetFactory: Sized {
 			if peer.is_major_syncing() || peer.network.num_queued_blocks() != 0 {
 				return Async::NotReady
 			}
-			match (highest, peer.client.info().chain.best_number) {
+			match (highest, peer.client.info().chain.best_hash) {
 				(None, b) => highest = Some(b),
 				(Some(ref a), ref b) if a == b => {},
 				(Some(_), _) => return Async::NotReady,

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

@@ -236,7 +236,14 @@ fn sync_no_common_longer_chain_fails() {
 	let mut net = TestNet::new(3);
 	net.peer(0).push_blocks(20, true);
 	net.peer(1).push_blocks(20, false);
-	net.block_until_sync(&mut runtime);
+	runtime.block_on(futures::future::poll_fn::<(), (), _>(|| -> Result<_, ()> {
+		net.poll();
+		if net.peer(0).is_major_syncing() {
+			Ok(Async::NotReady)
+		} else {
+			Ok(Async::Ready(()))
+		}
+	})).unwrap();
 	let peer1 = &net.peers()[1];
 	assert!(!net.peers()[0].blockchain_canon_equals(peer1));
 }
@@ -592,3 +599,37 @@ fn can_sync_explicit_forks() {
 		Ok(Async::Ready(()))
 	})).unwrap();
 }
+
+#[test]
+fn syncs_header_only_forks() {
+	let _ = ::env_logger::try_init();
+	let mut runtime = current_thread::Runtime::new().unwrap();
+	let mut net = TestNet::new(0);
+	let config = ProtocolConfig::default();
+	net.add_full_peer_with_states(&config, None);
+	net.add_full_peer_with_states(&config, Some(3));
+	net.peer(0).push_blocks(2, false);
+	net.peer(1).push_blocks(2, false);
+
+	net.peer(0).push_blocks(2, true);
+	let small_hash = net.peer(0).client().info().chain.best_hash;
+	let small_number = net.peer(0).client().info().chain.best_number;
+	net.peer(1).push_blocks(4, false);
+
+	net.block_until_sync(&mut runtime);
+	// Peer 1 won't sync the small fork because common block state is missing
+	assert_eq!(9, net.peer(0).blocks_count());
+	assert_eq!(7, net.peer(1).blocks_count());
+
+	// Request explicit header-only sync request for the ancient fork.
+	let first_peer_id = net.peer(0).id();
+	net.peer(1).set_sync_fork_request(vec![first_peer_id], small_hash, small_number);
+	runtime.block_on(futures::future::poll_fn::<(), (), _>(|| -> Result<_, ()> {
+		net.poll();
+		if net.peer(1).client().header(&BlockId::Hash(small_hash)).unwrap().is_none() {
+			return Ok(Async::NotReady)
+		}
+		Ok(Async::Ready(()))
+	})).unwrap();
+}
+

substrate/core/service/src/chain_ops.rs

@@ -156,6 +156,7 @@ macro_rules! import_blocks {
 						body: block.body,
 						justification: block.justification,
 						origin: None,
+						allow_missing_state: false,
 					}
 				]);
 			}

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

@@ -77,6 +77,7 @@ impl<B, E, RA, Block> ClientExt<Block> for Client<B, E, Block, RA>
 			finalized: false,
 			auxiliary: Vec::new(),
 			fork_choice: ForkChoiceStrategy::LongestChain,
+			allow_missing_state: false,
 		};
 
 		BlockImport::import_block(&mut (&*self), import, HashMap::new()).map(|_| ())
@@ -95,6 +96,7 @@ impl<B, E, RA, Block> ClientExt<Block> for Client<B, E, Block, RA>
 			finalized: false,
 			auxiliary: Vec::new(),
 			fork_choice: ForkChoiceStrategy::Custom(true),
+			allow_missing_state: false,
 		};
 
 		BlockImport::import_block(&mut (&*self), import, HashMap::new()).map(|_| ())
@@ -116,6 +118,7 @@ impl<B, E, RA, Block> ClientExt<Block> for Client<B, E, Block, RA>
 			finalized: true,
 			auxiliary: Vec::new(),
 			fork_choice: ForkChoiceStrategy::LongestChain,
+			allow_missing_state: false,
 		};
 
 		BlockImport::import_block(&mut (&*self), import, HashMap::new()).map(|_| ())

substrate/core/test-client/src/lib.rs

@@ -98,6 +98,12 @@ impl<Block, Executor, G: GenesisInit> TestClientBuilder<
 	pub fn backend(&self) -> Arc<Backend<Block>> {
 		self.backend.clone()
 	}
+
+	/// Create new `TestClientBuilder` with default backend and pruning window size
+	pub fn with_pruning_window(keep_blocks: u32) -> Self {
+		let backend = Arc::new(Backend::new_test(keep_blocks, 0));
+		Self::with_backend(backend)
+	}
 }
 
 impl<Executor, Backend, G: GenesisInit> TestClientBuilder<Executor, Backend, G> {

substrate/node-template/build.rs

@@ -1,5 +1,3 @@
-use std::{env, path::PathBuf};
-
 use vergen::{ConstantsFlags, generate_cargo_keys};
 
 const ERROR_MSG: &str = "Failed to generate metadata files";

substrate/node/cli/src/service.rs

@@ -523,6 +523,7 @@ mod tests {
 					finalized: true,
 					auxiliary: Vec::new(),
 					fork_choice: ForkChoiceStrategy::LongestChain,
+					allow_missing_state: false,
 				};
 
 				block_import.import_block(params, Default::default())

substrate/test-utils/transaction-factory/src/lib.rs

@@ -194,6 +194,7 @@ fn import_block<Backend, Exec, Block, RtApi>(
 		justification: None,
 		auxiliary: Vec::new(),
 		fork_choice: ForkChoiceStrategy::LongestChain,
+		allow_missing_state: false,
 	};
 	(&**client).import_block(import, HashMap::new()).expect("Failed to import block");
 }