Small tweaks to staking miner (#3460)

* Fix miner

* fix miner

* Update utils/staking-miner/src/monitor.rs

* Fix width

polkadot/utils/staking-miner/src/main.rs

@@ -299,7 +299,7 @@ async fn create_election_ext<T: EPM::Config, B: BlockT>(
 	with_staking: bool,
 ) -> Result<Ext, Error> {
 	use frame_support::{storage::generator::StorageMap, traits::PalletInfo};
-	let system_block_hash_key = <frame_system::BlockHash<T>>::prefix_hash();
+	use sp_core::hashing::twox_128;
 
 	Builder::<B>::new()
 		.mode(Mode::Online(OnlineConfig {
@@ -322,7 +322,8 @@ async fn create_election_ext<T: EPM::Config, B: BlockT>(
 			},
 			..Default::default()
 		}))
-		.inject_hashed_prefix(&system_block_hash_key)
+		.inject_hashed_prefix(&<frame_system::BlockHash<T>>::prefix_hash())
+		.inject_hashed_key(&[twox_128(b"System"), twox_128(b"Number")].concat())
 		.build()
 		.await
 		.map_err(|why| Error::RemoteExternalities(why))

polkadot/utils/staking-miner/src/monitor.rs

@@ -122,10 +122,21 @@ macro_rules! monitor_cmd_for { ($runtime:tt) => { paste::paste! {
 
 			let mut tx_subscription: Subscription<
 				TransactionStatus<<Block as BlockT>::Hash, <Block as BlockT>::Hash>
-			> = client
+			> = match client
 				.subscribe(&"author_submitAndWatchExtrinsic", params! { bytes }, "author_unwatchExtrinsic")
 				.await
-				.unwrap();
+			{
+				Ok(sub) => sub,
+				Err(why) => {
+				// This usually happens when we've been busy with mining for a few blocks, and now we're receiving the
+				// subscriptions of blocks in which we were busy. In these blocks, we still don't have a solution, so we
+				// re-compute a new solution and submit it with an outdated `Nonce`, which yields most often `Stale`
+				// error. NOTE: to improve this overall, and to be able to introduce an array of other fancy features,
+				// we should make this multi-threaded and do the computation outside of this callback.
+					log::warn!(target: LOG_TARGET, "failing to submit a transaction {:?}. continuing...", why);
+					continue
+				}
+			};
 
 			let _success = while let Some(status_update) = tx_subscription.next().await? {
 				log::trace!(target: LOG_TARGET, "status update {:?}", status_update);