Warp sync part II (#9284)

* Gap sync

* Gap epoch test

* Simplified network requests

* Update client/db/src/utils.rs

Co-authored-by: cheme <emericchevalier.pro@gmail.com>

* Fixed v1 migration and added some comments

* Next epoch is always regular

* Removed fork tree change

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Added a comment and converted assert to error

Co-authored-by: cheme <emericchevalier.pro@gmail.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

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

@@ -19,7 +19,7 @@
 use crate::error::Error;
 use codec::Encode;
 use futures::{future, prelude::*};
-use sc_client_api::{BlockBackend, UsageProvider};
+use sc_client_api::{BlockBackend, HeaderBackend};
 use sc_consensus::import_queue::ImportQueue;
 use sp_runtime::{generic::BlockId, traits::Block as BlockT};
 
@@ -33,7 +33,7 @@ pub fn check_block<B, IQ, C>(
 	block_id: BlockId<B>,
 ) -> Pin<Box<dyn Future<Output = Result<(), Error>> + Send>>
 where
-	C: BlockBackend<B> + UsageProvider<B> + Send + Sync + 'static,
+	C: BlockBackend<B> + HeaderBackend<B> + Send + Sync + 'static,
 	B: BlockT + for<'de> serde::Deserialize<'de>,
 	IQ: ImportQueue<B> + 'static,
 {

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

@@ -22,7 +22,7 @@ use futures::{future, prelude::*};
 use futures_timer::Delay;
 use log::{info, warn};
 use sc_chain_spec::ChainSpec;
-use sc_client_api::UsageProvider;
+use sc_client_api::HeaderBackend;
 use sc_consensus::import_queue::{
 	BlockImportError, BlockImportStatus, ImportQueue, IncomingBlock, Link,
 };
@@ -296,7 +296,7 @@ pub fn import_blocks<B, IQ, C>(
 	binary: bool,
 ) -> Pin<Box<dyn Future<Output = Result<(), Error>> + Send>>
 where
-	C: UsageProvider<B> + Send + Sync + 'static,
+	C: HeaderBackend<B> + Send + Sync + 'static,
 	B: BlockT + for<'de> serde::Deserialize<'de>,
 	IQ: ImportQueue<B> + 'static,
 {
@@ -438,7 +438,7 @@ where
 					info!(
 						"🎉 Imported {} blocks. Best: #{}",
 						read_block_count,
-						client.usage_info().chain.best_number
+						client.info().best_number
 					);
 					return Poll::Ready(Ok(()))
 				} else {
@@ -469,7 +469,7 @@ where
 
 		queue.poll_actions(cx, &mut link);
 
-		let best_number = client.usage_info().chain.best_number;
+		let best_number = client.info().best_number;
 		speedometer.notify_user(best_number);
 
 		if link.has_error {

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

@@ -684,8 +684,6 @@ where
 			..
 		} = import_block;
 
-		assert!(justifications.is_some() && finalized || justifications.is_none());
-
 		if !intermediates.is_empty() {
 			return Err(Error::IncompletePipeline)
 		}
@@ -779,11 +777,17 @@ where
 		}
 
 		let info = self.backend.blockchain().info();
+		let gap_block = info
+			.block_gap
+			.map_or(false, |(start, _)| *import_headers.post().number() == start);
+
+		assert!(justifications.is_some() && finalized || justifications.is_none() || gap_block);
 
 		// the block is lower than our last finalized block so it must revert
 		// finality, refusing import.
 		if status == blockchain::BlockStatus::Unknown &&
-			*import_headers.post().number() <= info.finalized_number
+			*import_headers.post().number() <= info.finalized_number &&
+			!gap_block
 		{
 			return Err(sp_blockchain::Error::NotInFinalizedChain)
 		}
@@ -854,12 +858,13 @@ where
 			None => None,
 		};
 
-		let is_new_best = finalized ||
-			match fork_choice {
-				ForkChoiceStrategy::LongestChain =>
-					import_headers.post().number() > &info.best_number,
-				ForkChoiceStrategy::Custom(v) => v,
-			};
+		let is_new_best = !gap_block &&
+			(finalized ||
+				match fork_choice {
+					ForkChoiceStrategy::LongestChain =>
+						import_headers.post().number() > &info.best_number,
+					ForkChoiceStrategy::Custom(v) => v,
+				});
 
 		let leaf_state = if finalized {
 			NewBlockState::Final