Rework the event system of sc-network (#1370)

This commit introduces a new concept called `NotificationService` which
allows Polkadot protocols to communicate with the underlying
notification protocol implementation directly, without routing events
through `NetworkWorker`. This implies that each protocol has its own
service which it uses to communicate with remote peers and that each
`NotificationService` is unique with respect to the underlying
notification protocol, meaning `NotificationService` for the transaction
protocol can only be used to send and receive transaction-related
notifications.

The `NotificationService` concept introduces two additional benefits:
  * allow protocols to start using custom handshakes
  * allow protocols to accept/reject inbound peers

Previously the validation of inbound connections was solely the
responsibility of `ProtocolController`. This caused issues with light
peers and `SyncingEngine` as `ProtocolController` would accept more
peers than `SyncingEngine` could accept which caused peers to have
differing views of their own states. `SyncingEngine` would reject excess
peers but these rejections were not properly communicated to those peers
causing them to assume that they were accepted.

With `NotificationService`, the local handshake is not sent to remote
peer if peer is rejected which allows it to detect that it was rejected.

This commit also deprecates the use of `NetworkEventStream` for all
notification-related events and going forward only DHT events are
provided through `NetworkEventStream`. If protocols wish to follow each
other's events, they must introduce additional abtractions, as is done
for GRANDPA and transactions protocols by following the syncing protocol
through `SyncEventStream`.

Fixes https://github.com/paritytech/polkadot-sdk/issues/512
Fixes https://github.com/paritytech/polkadot-sdk/issues/514
Fixes https://github.com/paritytech/polkadot-sdk/issues/515
Fixes https://github.com/paritytech/polkadot-sdk/issues/554
Fixes https://github.com/paritytech/polkadot-sdk/issues/556

---
These changes are transferred from
https://github.com/paritytech/substrate/pull/14197 but there are no
functional changes compared to that PR

---------

Co-authored-by: Dmitry Markin <dmitry@markin.tech>
Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>

cumulus/client/relay-chain-minimal-node/src/network.rs

@@ -26,10 +26,9 @@ use sc_network::{
 	NetworkService,
 };
 
-use sc_network::config::FullNetworkConfiguration;
+use sc_network::{config::FullNetworkConfiguration, NotificationService};
 use sc_network_common::{role::Roles, sync::message::BlockAnnouncesHandshake};
 use sc_service::{error::Error, Configuration, NetworkStarter, SpawnTaskHandle};
-use sc_utils::mpsc::tracing_unbounded;
 
 use std::{iter, sync::Arc};
 
@@ -45,7 +44,7 @@ pub(crate) fn build_collator_network(
 	Error,
 > {
 	let protocol_id = config.protocol_id();
-	let block_announce_config = get_block_announce_proto_config::<Block>(
+	let (block_announce_config, _notification_service) = get_block_announce_proto_config::<Block>(
 		protocol_id.clone(),
 		&None,
 		Roles::from(&config.role),
@@ -69,8 +68,6 @@ pub(crate) fn build_collator_network(
 	let peer_store_handle = peer_store.handle();
 	spawn_handle.spawn("peer-store", Some("networking"), peer_store.run());
 
-	// RX is not used for anything because syncing is not started for the minimal node
-	let (tx, _rx) = tracing_unbounded("mpsc_syncing_engine_protocol", 100_000);
 	let network_params = sc_network::config::Params::<Block> {
 		role: config.role.clone(),
 		executor: {
@@ -86,7 +83,6 @@ pub(crate) fn build_collator_network(
 		protocol_id,
 		metrics_registry: config.prometheus_config.as_ref().map(|config| config.registry.clone()),
 		block_announce_config,
-		tx,
 	};
 
 	let network_worker = sc_network::NetworkWorker::new(network_params)?;
@@ -150,7 +146,7 @@ fn get_block_announce_proto_config<B: BlockT>(
 	best_number: NumberFor<B>,
 	best_hash: B::Hash,
 	genesis_hash: B::Hash,
-) -> NonDefaultSetConfig {
+) -> (NonDefaultSetConfig, Box<dyn NotificationService>) {
 	let block_announces_protocol = {
 		let genesis_hash = genesis_hash.as_ref();
 		if let Some(ref fork_id) = fork_id {
@@ -160,12 +156,11 @@ fn get_block_announce_proto_config<B: BlockT>(
 		}
 	};
 
-	NonDefaultSetConfig {
-		notifications_protocol: block_announces_protocol.into(),
-		fallback_names: iter::once(format!("/{}/block-announces/1", protocol_id.as_ref()).into())
-			.collect(),
-		max_notification_size: 1024 * 1024,
-		handshake: Some(NotificationHandshake::new(BlockAnnouncesHandshake::<B>::build(
+	NonDefaultSetConfig::new(
+		block_announces_protocol.into(),
+		iter::once(format!("/{}/block-announces/1", protocol_id.as_ref()).into()).collect(),
+		1024 * 1024,
+		Some(NotificationHandshake::new(BlockAnnouncesHandshake::<B>::build(
 			roles,
 			best_number,
 			best_hash,
@@ -173,11 +168,11 @@ fn get_block_announce_proto_config<B: BlockT>(
 		))),
 		// NOTE: `set_config` will be ignored by `protocol.rs` as the block announcement
 		// protocol is still hardcoded into the peerset.
-		set_config: SetConfig {
+		SetConfig {
 			in_peers: 0,
 			out_peers: 0,
 			reserved_nodes: Vec::new(),
 			non_reserved_mode: NonReservedPeerMode::Deny,
 		},
-	}
+	)
 }