Sync block justifications (#1410)

* core: sync protocol for justifications

* core: basic test for justification sync

* core: pass block number with justification

* grandpa: request justifications when importing change blocks

* core: pass finality notifications to chain sync

* core: require justifications for pending change blocks on start

* core: avoid requesting justifications from previous failed peers

* core: timeout block justification requests

* core: add some docs

* core: fix unused variables warning

* core: tick pending justifications fetch periodically

* grandpa: add test for syncing justifications

* core: early exit dispatch of pending justifications

* core: style fix

* core: grandpa: change logging level

* core: sync: add missing docs

* core: network: report peer on bad justification

* core: replace mem::replace with Option::take

* core: revert authority set changes on failed block finalization

* core: grandpa: add docs to import_justification

* core: warn on re-finalization of last finalized block

* core: only notify sync with last finality notification

* core: style fix

* core: add docs for PendingJustifications

* core: network: use BlockRequest messages for justification requests

* core: reference issues in todo comments

* core: grandpa: revert authority set changes on db

* core: grandpa: remove inconsistent state warning

substrate/core/network/src/service.rs

@@ -94,6 +94,10 @@ impl<B: BlockT, E: ExecuteInContext<B>> Link<B> for NetworkLink<B, E> {
 		self.with_sync(|sync, _| sync.block_imported(&hash, number))
 	}
 
+	fn request_justification(&self, hash: &B::Hash, number: NumberFor<B>) {
+		self.with_sync(|sync, protocol| sync.request_justification(hash, number, protocol))
+	}
+
 	fn maintain_sync(&self) {
 		self.with_sync(|sync, protocol| sync.maintain_sync(protocol))
 	}
@@ -174,6 +178,11 @@ impl<B: BlockT + 'static, S: NetworkSpecialization<B>, H: ExHashT> Service<B, S,
 		self.handler.on_block_imported(&mut NetSyncIo::new(&self.network, self.protocol_id), hash, header)
 	}
 
+	/// Called when a new block is finalized by the client.
+	pub fn on_block_finalized(&self, hash: B::Hash, header: &B::Header) {
+		self.handler.on_block_finalized(&mut NetSyncIo::new(&self.network, self.protocol_id), hash, header)
+	}
+
 	/// Called when new transactons are imported by the client.
 	pub fn trigger_repropagate(&self) {
 		self.handler.propagate_extrinsics(&mut NetSyncIo::new(&self.network, self.protocol_id));